The first thing I would do is make it Dell's problem. Their customer service is better than most and if you are running XP it's probably still covered.

Have you run scandisk? Maybe disk cleanup tanks when it's trying to delete a file that is corrupted. Also, get the latest drivers for your motherboard and video card.

If that doesn't help, I would consider a fresh start. This would involve backing up the entire drive and reimaging it as it came from Dell. Then you would download the latest drivers and use the backup to restore your personal files. This is a big project, though.

It's possible that it's a hardware problem, too. A failing hard drive or too much heat in the case could cause random lock-ups. Good luck and keep posting back.