Hardlocks in Windows XP?

I get frequent hardlocks in XP, and I've tried every thing I can think of. Individual RAM testing shows that the RAM itself is fine, I removed all hardware (and tried 2 different video cards) to no avail. Now I just reformatted and I still get the hardlocks.

They occur whenever I'm downloading a file or strain is being put on the processor.

This leads me to believe it is a processor error, any way I can test this hypothesis?

>>7

Any computer parts supplier should be able to supply thermal compound - look in their CPU cooling/accessories section. Since you've already taken the heatsink off, I'd strongly recommend a new coat of thermal compound anyway (remembering to clean the old stuff off both the heatsink and the CPU's heat spreader first, of course) - putting it back and just leaving the old thermal gunk on there won't be as good.