I suppose it's possible the power supply is to blame, but it doesn't seem like a coincidence with the memory. With 1-of-3 sticks in, I can't do anything at all to crash my computer. I can play 5 flash videos at once, game at 2560x1600 and graphics settings at max, and anything else. I can leave the system running for a week straight (or however long I like). But with all three sticks in, the first flash video I play crashes the computer, without fail.

I've swapped those other two sticks in and out a half dozen times now, and the results are consistent. 2GB - fine. 6GB - crash. I just can't figure out why. I'm willing to take a look at other components, but I don't have any replacements for any of them...