First - make sure you have the latest hardware drivers for each of your
hardware compoentns...
Chipset (motherboard), Network Card (and/or modem), Video Card and Sound
Card at least.
You would visit the actual manufacturer's support web pages and download the
driver for the particular card/board you have and install each one yourself.

After that - sure - you could download all of the patches and install them
yourself.  You could even integrat the majority of them into your
installation CD.

Each month Microsoft releases that month's updates in ISO format:
January 2006-current
http://support.microsoft.com/kb/913086

If you are more trusting:

AutoPatcher
http://www.autopatcher.com/

Windows Updates Downloader
http://wud.jcarle.com/

You can download each update manually - based off the KB Article number,
etc.  That way you can back it up/burn a CD of them in case you need them or
use them to keep a slipstream/integrated (updated) Windows XP CD.

How to use the Windows Update Catalog
http://support.microsoft.com/kb/323166
(In order to use the Windows Update Catalog, you must use IE to get the
patches..)

Integrate software updates into your Windows installation source files
http://support.microsoft.com/kb/828930

Really customize your CD..
http://unattended.msfn.org/

Produce an up-to-date XP Distribution CD
http://xpcreate.com/

AutoStreamer
http://www.neowin.net/forum/index.php?showtopic=223562

You can see the critical (security and other) patches released for a given
month using the following:

http://www.microsoft.com/technet/security/bulletin/ms##-***.mspx

At the end of this line you see "ms##-***.mspx" ..  If you simply replace ##
with the two-digit year and the *** with the three character month
abbreviation, you will see the list of "critical" and "important" patches
for that month (since it only happens once a month usually, if you check by
the second Tuesday (wait until afternoon) of each month - you should be
fine) - note that future months will not work.

As an example...

December 2004's patches..
http://www.microsoft.com/technet/security/bulletin/ms04-dec.mspx

March 2005's patches..
None released.. so that one will fail...

May 2006's patches..
http://www.microsoft.com/technet/security/bulletin/ms06-may.mspx

January 2007's patches..
http://www.microsoft.com/technet/security/bulletin/ms07-jan.mspx

Once you get on the page with each month's list of patches.. You can go to
the related KB articles and grab the appropriate files from there.

Need Microsoft Office updates?
http://office.microsoft.com/en-us/downloads/maincatalog.aspx

Here's a list of updates from SP2 until about April 2007 to get you
started...

Direct Download of Service Pack 2 (SP2) for Windows XP
http://snipurl.com/8bqy

Critical Updates
----------------------
Released: -- [ Web Page Address ] -- Description:
9/14/2004 -- [ http://support.microsoft.com/kb/885626 ]
 -- Critical Update for Windows XP
11/22/2004 -- [ http://support.microsoft.com/kb/887742 ]
 -- Update for Windows XP
12/13/2004 -- [ http://support.microsoft.com/kb/885835 ]
 -- Security Update for Windows XP
12/13/2004 -- [ http://support.microsoft.com/kb/885836 ]
 -- Security Update for Windows XP
12/13/2004 -- [ http://support.microsoft.com/kb/886185 ]
 -- Critical Update for Windows XP
12/13/2004 -- [ http://support.microsoft.com/kb/873339 ]
 -- Security Update for Windows XP
2/7/2005 -- [ http://support.microsoft.com/kb/891781 ]
 -- Security Update for Windows XP
2/7/2005 -- [ http://support.microsoft.com/kb/888302 ]
-- Security Update for Windows XP
2/7/2005 -- [ http://support.microsoft.com/kb/887472 ]
 -- Security Update for Windows Messenger
4/11/2005 -- [ http://support.microsoft.com/kb/890859 ]
 -- Security Update for Windows XP
5/18/2005 -- [ http://support.microsoft.com/kb/894391 ]
 -- Update for Windows XP
5/24/2005 -- [ http://support.microsoft.com/kb/896344 ]
 -- Update for Windows XP
6/13/2005 -- [ http://support.microsoft.com/kb/896358 ]
 -- Security Update for Microsoft Windows XP
6/13/2005 -- [ http://support.microsoft.com/kb/896428 ]
 -- Security Update for Windows XP
6/24/2005 -- [ http://support.microsoft.com/kb/900930 ]
 -- Update for Windows XP
6/27/2005 -- [ http://support.microsoft.com/kb/898461 ]
 -- Update for Windows XP
7/11/2005 -- [ http://support.microsoft.com/kb/901214 ]
 -- Security Update for Windows XP
8/8/2005 -- [ http://support.microsoft.com/kb/896423 ]
 -- Security Update for Windows XP
8/8/2005 -- [ http://support.microsoft.com/kb/899587 ]
 -- Security Update for Windows XP
8/8/2005 -- [ http://support.microsoft.com/kb/899591 ]
 -- Security Update for Windows XP
8/8/2005 -- [ http://support.microsoft.com/kb/893756 ]
 -- Security Update for Windows XP
10/10/2005 -- [ http://support.microsoft.com/kb/901017 ]
 -- Security Update for Windows XP
10/10/2005 -- [ http://support.microsoft.com/kb/902400 ]
 -- Security Update for Windows XP
10/10/2005 -- [ http://support.microsoft.com/kb/905749 ]
-- Security Update for Windows XP
10/10/2005 -- [ http://support.microsoft.com/kb/905414 ]
 -- Security Update for Windows XP
10/10/2005 -- [ http://support.microsoft.com/kb/900725 ]
 -- Security Update for Windows XP
12/12/2005 -- [ http://support.microsoft.com/kb/910437 ]
 -- Update for Windows XP
12/13/2005 -- [ http://support.microsoft.com/kb/904706 ]
 -- Security Update for Windows XP
1/9/2006 -- [ http://support.microsoft.com/kb/908519 ]
-- Security Update for Windows XP
2/13/2006 -- [ http://support.microsoft.com/kb/911927 ]
 -- Security Update for Windows XP
4/10/2006 -- [ http://support.microsoft.com/kb/911562 ]
 -- Security Update for Windows XP
4/18/2006 -- [ http://support.microsoft.com/kb/904942 ]
-- Update for Windows XP
4/25/2006 -- [ http://support.microsoft.com/kb/900485 ]
 -- Update for Windows XP
4/25/2006 -- [ http://support.microsoft.com/kb/908531 ]
 -- Security Update for Windows XP
5/9/2006 -- [ http://support.microsoft.com/kb/913580 ]
 -- Security Update for Windows XP
6/6/2006 -- [ http://support.microsoft.com/kb/916595 ]
 -- Update for Windows XP
6/8/2006 -- [ http://support.microsoft.com/kb/918439 ]
 -- Vulnerability in ART Image Rendering Could Allow Remote Code
     Execution in Internet Explorer for Windows XP SP2
6/12/2006 -- [ http://support.microsoft.com/kb/914389 ]
 -- Security Update for Windows XP
6/12/2006 -- [ http://support.microsoft.com/kb/917953 ]
 -- Security Update for Windows XP
6/13/2006 -- [ http://support.microsoft.com/kb/917344 ]
 -- JScript 5.6 Security Update for Windows XP SP1 and SP2
6/27/2006 -- [ http://support.microsoft.com/kb/911280 ]
 -- Security Update for Windows XP
7/10/2006 -- [ http://support.microsoft.com/kb/917159 ]
 -- Security Update for Windows XP
7/10/2006 -- [ http://support.microsoft.com/kb/914388 ]
 -- Security Update for Windows XP
8/7/2006 -- [ http://support.microsoft.com/kb/917422 ]
 -- Security Update for Windows XP
8/7/2006 -- [ http://support.microsoft.com/kb/920670 ]
 -- Security Update for Windows XP
8/7/2006 -- [ http://support.microsoft.com/kb/922616 ]
 -- Security Update for Windows XP
8/7/2006 -- [ http://support.microsoft.com/kb/920683 ]
 -- Security Update for Windows XP
8/17/2006 -- [ http://support.microsoft.com/kb/920872 ]
 -- Update for Windows XP
9/11/2006 -- [ http://support.microsoft.com/kb/920685 ]
 -- Security Update for Windows XP
9/11/2006 -- [ http://support.microsoft.com/kb/922582 ]
 -- Update for Windows XP
9/11/2006 -- [ http://support.microsoft.com/kb/919007 ]
 -- Security Update for Windows XP
10/9/2006 -- [ http://support.microsoft.com/kb/922819 ]
 -- Security Update for Windows XP
10/9/2006 -- [ http://support.microsoft.com/kb/924496 ]
 -- Security Update for Windows XP
10/9/2006 -- [ http://support.microsoft.com/kb/923414 ]
 -- Security Update for Windows XP
10/9/2006 -- [ http://support.microsoft.com/kb/923191 ]
 -- Security Update for Windows XP
11/14/2006 -- [ http://support.microsoft.com/kb/920213 ]
 -- Vulnerability in Microsoft Agent could allow remote code
    execution
11/14/2006 -- [ http://support.microsoft.com/kb/923789 ]
 -- Vulnerabilities in Macromedia Flash Player from Adobe
    could allow remote code execution
11/14/2006 -- [ http://support.microsoft.com/kb/924270 ]
 -- Vulnerability in Workstation Service could allow
    remote code execution
11/14/2006 -- [ http://support.microsoft.com/kb/928088 ]
 -- Vulnerability in Microsoft XML Core Services could
    allow remote code execution
11/14/2006 -- [ http://support.microsoft.com/kb/923980 ]
 -- Vulnerability in the Client Service could allow remote code
    execution
12/12/2006 -- [ http://support.microsoft.com/kb/926247 ]
 -- Vulnerability in Simple Network Management Protocol (SNMP)
    could allow remote code execution
12/12/2006 -- [ http://support.microsoft.com/kb/926255 ]
 -- Vulnerability in Windows could allow elevation of privilege
12/12/2006 -- [ http://support.microsoft.com/kb/923694 ]
 -- Cumulative security update for Outlook Express
1/9/2007 -- [ http://support.microsoft.com/kb/929969 ]
 -- Vulnerability in Vector Markup Language
    Could Allow Remote Code Execution
 * If you have installed IE7, also install the IE7 version
   of this patch!
2/13/2007 -- [ http://support.microsoft.com/kb/928255 ]
 -- Vulnerability in Windows Shell Could Allow Elevation
    of Privilege
2/13/2007 -- [ http://support.microsoft.com/kb/927802 ]
 -- Vulnerability in Windows Image Acquisition Service
    Could Allow Elevation of Privilege
2/13/2007 -- [ http://support.microsoft.com/kb/928843 ]
 -- Vulnerability in HTML Help ActiveX Control Could
    Allow Remote Code Execution
2/13/2007 -- [ http://support.microsoft.com/kb/927779 ]
 -- Vulnerability in Microsoft Data Access Components
    Could Allow Remote Code Execution
2/13/2007 -- [ http://support.microsoft.com/kb/926436 ]
 -- Vulnerability in Microsoft OLE Dialog Could Allow
    Remote Code Execution
2/13/2007 -- [ http://support.microsoft.com/kb/924667 ]
 -- Vulnerability in Microsoft MFC Could Allow Remote
    Code Execution
2/13/2007 -- [ http://support.microsoft.com/kb/918118 ]
 -- Vulnerability in Microsoft RichEdit Could Allow
    Remote Code Execution
2/13/2007 -- [ http://support.microsoft.com/kb/928090 ]
 -- Cumulative Security Update for Internet Explorer
 * If you have IE7, obtain that version of this update.
4/3/2007 -- [ http://support.microsoft.com/kb/925902 ]
 -- Vulnerabilities in GDI Could Allow Remote Code Execution
4/10/2007 -- [ http://support.microsoft.com/kb/931261 ]
 -- Vulnerability in Universal Plug and Play Could
    Allow Remote Code Execution
4/10/2007 -- [ http://support.microsoft.com/kb/932168 ]
 -- Vulnerability in Microsoft Agent Could Allow Remote
    Code Execution
4/10/2007 -- [ http://support.microsoft.com/kb/930178 ]
 -- Vulnerabilities in CSRSS Could Allow Remote Code
    Execution
4/10/2007 -- [ http://support.microsoft.com/kb/931784 ]
 -- Vulnerability in Windows Kernel Could Allow
    Elevation of Privilege

Media Player:
-------------------
Released: -- [ Web Page Address: ] -- Description:
9/2/2004 -- [ http://go.microsoft.com/fwlink/?LinkId=30984 ]
-- Windows Media Player 10
11/7/2005 -- [ http://support.microsoft.com/kb/902344 ]
 -- Update for WMDRM-enabled Media Players
2/13/2006 -- [ http://support.microsoft.com/kb/911564 ]
 -- Security Update for Windows Media Player Plug-in
4/11/2006 -- [ http://support.microsoft.com/kb/911565 ]
 -- Security Update for Windows Media Player 10 for Windows XP
6/12/2006 -- [ http://support.microsoft.com/kb/917734 ]
 -- Security Update for Windows Media Player 10 for Windows XP
12/12/2006 -- [ http://support.microsoft.com/kb/923689 ]
 -- Vulnerability in Windows Media Format Could Allow Remote
    Code Execution

.NET Framework:
------------------------
Released: -- [ Web Page Address: ] -- Description:
3/30/2004 -- [ http://snipurl.com/10bde ]
 -- Microsoft .NET Framework Version 1.1 Redistributable Package
8/30/2004 -- [ http://support.microsoft.com/kb/885055 ]
 -- Microsoft .NET Framework 1.1 Service Pack 1
2/8/2005 -- [ http://support.microsoft.com/kb/887219 ]
 -- ASP.NET Security Update for Microsoft NET Framework 1.1
    Service Pack 1
3/22/2006 -- [ http://snipurl.com/10bdv ]
 -- Microsoft .NET Framework Version 2.0 Redistributable
     Package (x86)
7/11/2006 -- [ http://support.microsoft.com/kb/917283 ]
 -- NDP 2.0 ASP.Net Security Update
10/10/2006 -- [ http://support.microsoft.com/kb/922770 ]
 -- NET Framework 2.0 SYSTEM.WEB.DLL Security Update

Other Updates:
---------------------
Released: -- [ Web Page Address: ] -- Description:
9/14/2004 -- [ http://support.microsoft.com/kb/873374 ]
 -- Microsoft GDI+ Detection Tool
9/2/2005 -- [ http://support.microsoft.com/kb/893803 ]
 -- Windows Installer 3.1 Redistributable (v2)
10/14/2005 -- [ http://snipurl.com/10bex ]
 -- Windows Media Connect 2.0
11/29/2005 -- [ http://support.microsoft.com/kb/909520 ]
 -- Microsoft Base Smart Card Cryptographic Service Provider
     Package: x86
10/10/2006 -- [ http://support.microsoft.com/kb/890830 ]
 -- Microsoft® Windows® Malicious Software Removal Tool
     - November 2006

Purely OPTIONAL:
----------------------
10/18/2006 -- [ http://www.microsoft.com/windows/ie/downloads/ ]
 -- Internet Explorer 7.0
10/30/2006 -- [ http://snipurl.com/167ea ]
 -- Media Player 11
12/8/2006 -- [ http://support.microsoft.com/kb/925876 ]
 -- Remote Desktop Connection 6.0 client

There's a strong possibility you *don't* need to reinstall XP.

What particular problems have you been experiencing?