Do xp repair, you get to keep your data and programs. Boot off xp disk, do not take the first offer to go to a repair console. Do setup xp. then do what it says like accept the license etc., soon you get a screen showing where your installation currently resides (presumably c:\windows). At that time press the key that the screen says for a repair (r maybe???). From there it looks like you are doing a fresh install, except you don't format or anything like that.
I'm going by memory, so if this does not make sense, reply and I'll do it tonight and clear things up, or perhaps someone can fill in what I missed.
I have a 100% success rate of preserving data doing this, and a 75% rate of solving xp problems.
Much simpler, but less effective is to open a cmd window and type "sfc /scannow"
Here's some good bedtime reading and you might even get luck (keep this clean guys) and find an sp3 version if you search MS site:
http://support.microsoft.com/default.aspx?scid=kb;en-us;875355&Product=windowsxpsp2
Edit: you might end up doing a reinstall, but the repair only takes an hour, mostly unattended. So it's worth a try. Also, you keep drivers, net setup, accounts and all the little things that make reinstall a nightmare for many.
Edit2: On behalf of Tater Salad, my avitar and best friend, DIE FLEAS DIE!!!
Cherio