I use a screen saver - but from my experience this has only happened when I'm sitting at the computer TRYING to get stuff done when it locks up. I did check my power settings, and nothing shuts down, ever. Not that I would expect it to when using it, but I checked it anyway.
I don't recall it ever occuring when idle, i.e. when I left it for a bit and came back to it. Also, I don't use A/V (but I have done scans to be sure that's not the case). To further that point, it happens on my laptop too, which does have A/V.
Just loaded Process Lasso a few minutes ago. Nifty tool, will see if it comes up with anything. I'm overly disappointed there isn't some other way to try and find out what's going on natively within Vista, but from what I have read Windows 7 is taking diagnostics to a new level. Will have to see what that really means.
Theoretically this tool should prevent my problem from ever happening again, as well as pointing out the problem. Here is to hoping it works as advertised :up: