Remember when I was getting all those strange crashes when trying to encode MOV files? And the crashes were both on the PC and the Mac?

If you followed that thread, you'll recall that the Mac side of the problem was having installed the Divx codec, and the PC side of the problem was a bad RAM stick whose symptoms didn't show up until after a few passes into Memtest.

I got the replacement RAM stick for the PC. The bad one was part of a matched pair of Corsair PC3700. The replacement they sent me was PC4000.

I'm putting them in the paired slots, and all seems OK at first, memtest passes several passes, but I can't run any 3D video game for more than 10 minutes without a crash, even after rolling back to known-good video drivers.

Is it possible that having the mismatched pair is the issue? What happens when you have paired RAM sticks that are two different speed ratings like that?