Have you tried running System File Checker? If not pop your XP CD into the
drive and exit the menu screen that pops up. Click on the Start button and
select Run. Enter the following and click the OK button

SFC /SCANNOW

*note: there is a space between "SFC" and "/". System File Checker will do a
search of your system for corrupt system files and replace them from files
on the CD as well as newer files from service packs on your hard drive.
Unfortunately it doesn't tell you when or if it has found and replaced
anything. SFC /SCANNOW takes up to 20 minutes to run so be patient as there
is a progress bar. When it is finished try rebooting your computer and see
if the problems you are experiencing are fixed.

You can also look for individual Windows Components through Control
Panel->Add/Remove Programs->Add Windows Components.

You can first try the System File Checker:
Start>Run>sfc /scannow [enter]

If that doesn't work, you can try a Repair Install:
http://www.michaelstevenstech.com/XPrepairinstall.htm

A Repair Install should not affect your programs and data; however, it is
always wise to have current backups.

Malke