I feel your pain. I just got my computer back from the shop because one of the kids getting on Myspace and downloading a adware from hell. It cost me about $90 bucks to reinstall XP and another $35 for them to back up and reinstall the files. I think I had about 8 gigs of files to backup, I could have never done that muself. The real kicker was I had to reinstall every program from scratch Which was a pain in the rear.
A while back my machine was freezing like what you describe and it was the mouse had gone bad I bought a new mouse and that cured it. That was until the new Mouse had a USB conflict with another program and it started freezing up again. Arn't computers wonderfull?