This is a description of the causes, but if you have not recently installed any new hardware, I would hazard a guess at your Hard drive.
Your boot hdd may well be dying, so best thing to do is to backup all critical data before you do anything else.
If you HAVE installed new kit, then it may well be the culprit as the article explains.
You could try a system restore back to a time prior to seeing the BSOD, or a repair install of XP.
Repair install (leaving data intact):
Step by step.