Crap! Looks like my 8800GTX video card is broken. That's a serious bummer.
The card does some very serious funny things: as soon as going in-game, the card doesn't really freeze up, but has some sort of memory corruption problem, which remains throughout reboots.
Very coincidentally, I just ordered new hardware for my new gaming computer. The only thing not being replaced was the video card, because I thought it would be better to just wait a while until the next generation of cards from nVidia were available.
Apparently, Fate has decided otherwise.