Check the Windows 7 compatibility website
FIRST! You may have hardware that won't work in Win7, like a video card (old AGP), or printer.
Seem MANY people upset with Windows 7, 'cause this or that doens't work, but they didn't run the "checker" before installing, much less buying it!
Best of all, do you have the Windows XP install disk(s), to SP3? It might have a recovery program on it, like 7 does.....I can't believe I don't know this!