My friends have only had problems with games crashing on their computers at first, but no, I don't have Vista. Otherwise, if the display flickers every now and again, it could be refeshment of the desktop/screen, a faulty graphics driver, bad hardware (can also cause the lock-ups), viruses, and for lock-ups, the computer could be a bit slow, or it could be overheating. My friend's laptop freezes up when it gets too hot and he's playing games on his bed.
Also, how much RAM do you have? If Aero is on and you only have a gig of RAM and you have a lot of programs open, Aero might be using too many resources. Try turning off Aero and see if that helps things up a bit.