I have the same sort of issue, after a certain amount of time I start to see corrupted textures, and will crash very shortly after that. It started after one of the critical updates, I went from one crash per week, to one every two hours or so.
I'm assuming it's a conflict between vista and my graphics drivers, to do with how ATI cards handle texturing. Since it seems to be a vista problem not one with my card, new drivers don't help in my case.
I'm curious if this is similar to your problem, Heretic.