I wrote about this in another thread. its usually when I'm loading something, or doing something that stresses the PC. The main thing is when I start programs like Everest: Home or 3DMark03 and 3DMark05, it totally freezes when the loading window comes up. For Everest, it ALWAYS freezes when its "Scanning PCI devices." My FX 5200 is a PCI card, so thats a suspect. Other times its frozen are during gameplay in BF2 and Sims 2. My sister, who also uses my comp, has said that it freezes for her everytime she loads her character on TOONTOWN! Thats like the lowest requirement game out there!
Before and while I installed windows, It would freeze when the "Setup is starting windows 2000" came up. Again, the comp was starting something. it would also freeze when I was installing my Ultra ATA drive.
Also, my processor is at high-40s to low 50s degrees in Celcius. Thats my other suspect. My major suspect actually.