Blue screen from overheating is generally an easy fix,
1. unplug the machine,
2. clean out the dust bunnies w/ compressed air,
3. clean off and replace the thermal paste on the chip,
4. w/ the case open plug it in, switch it on and see that all the fans are running.
If over temp is the problem that's it Gary, 10 min job. Geek squad will get you 100 bux and do there best to sell you a new compy.
Personally I wouldn't mess with a PC that dated for every day use. Apply the 100 saved to the cost of a cheap notebook, pull the hard drive from your XP machine and use an adaptor to pull the information you want from it, done deal.
I just did a quick search and came up with this for best price on refurbs with win7
http://www.newegg.com/Product/ProductLi ... sdeptsrh=1