This sounds like it might be a possible problem with your system memory. To rule this out, download the following Microsoft memory diagnostic from:
and create a bootable test cd. Make sure your bios is configured to boot from CD and let the test run overnight.
I've used this program in the past to find bad memory in my system. It found the problem almost immediately after I began running it, while Memtst86 (another popular memory diagnostic) did not.