could be the DNS issue. this may help. quoted from
http://www.howtonetworking.com/winslow.htm
Why is XP running slower while logon 1

When I login into a Windows 2000 active directory from a new xp pro machine
the login in is extremely slow.  After logged on, everything works fine. But
other windows versions don't have this problem.
A: This is almost like name resolution issue. Comparing with previous
versions, XP is heavily dependent on DNS to find DC. If the DNS is
configured incorrectly, XP will take longer time waiting for it to timeout
before it tries using NetBIOS. Make sure
1) The DNS setup correct and have the server information.
2) XP clients can find the DNS server.
3) XP machine's DNS server is pointed to your internal DNS server rather
than your ISP's DNS server.
4) Make sure no errors on logon  scripts  or  GPO's  that  could  be causing
the  delay.
5) Check any errors on event viewer.
6) Disable NetBIOS on the interfaces that client will not use.

Are you logging into a Domain on the server?
If so, then slow logins usually indicate a DNS misconfiguration...

XP differs from previous versions of windows in that it uses
DNS as it's primary name resolution method for finding domain
controllers:

How Domain Controllers Are Located in Windows XP
http://support.microsoft.com/default.aspx?scid=kb;en-us;314861

If DNS is misconfigured, XP will spend a lot of time waiting for it to
timeout before it tries using legacy NT4 sytle NetBIOS.
( Which may or may not work. )

1) Ensure that the XP clients are all configured to point to the local
  DNS server which hosts the AD domain. That will probably be the
  win2k server itself.
  They should NOT be pointing an an ISP's DNS server.
  An 'ipconfig /all' on the XP box should reveal ONLY the domain's
  DNS server.

  ( you should use the DHCP server to push out the local DNS server
  address. )

2) Ensure DNS server on win2k is configured to permit dynamic updates.

3) Ensure the win2k server points to itself as a DNS server.

4) For external ( internet ) name resolution, specify your ISP's DNS server
  not on the clients, but in the 'forwarders' tab of the local win2k DNS
server.

On the DNS server, if you cannot access the 'Forwarders' and 'Root Hints'
tabs because they are greyed out, that is because there is a root zone (".")
present on the DNS server.   You MUST delete this root zone to permit the
server to forward unresolved queries to yout ISP or the root servers:

HOWTO: Remove the Root Zone (Dot Zone)
http://support.microsoft.com/default.aspx?kbid=298148

The following articles may assist you in setting up DNS correctly:

Setting Up the Domain Name System for Active Directory
http://support.microsoft.com/default.aspx?scid=kb;en-us;237675
HOW TO: Configure DNS for Internet Access in Windows 2000
http://support.microsoft.com/default.aspx?scid=kb;en-us;300202