I said in the initial post that "I ran memtest86 overnight"

Christian: I have not tried rotating the memory sticks. That's a good idea. And fortunately (or unfortunately), it should be pretty easy to test. Either the computer locks up on the first flash video I play or it doesn't.

I should have mentioned in the first post that I'm currently running Windows 7 64. However, it's only the 7100 build. I plan on installing the 7600 build in the next few days to make sure that isn't the problem.