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#31
If there was absolutely nothing not on the win 7 DVD installed, then it has to be the memory itself. I know you ran memtest but you may have to go back and re-run it for more passes, or run each stick individually, etc.
If there was nothing but the win 7 dvd installed (not even malware) then it has to be hardware. Since it is memory corruption the first thing to check is the memory.