There are quite a number of people affected by this, me included. Its been around a year already and no comments from nVidia, nor are there any one-true solution. The cause is even just being speculated. Some solved theirs, but again, each solution is different(underclocking, overclocking, change motherboard, etc.)... Its being talked about at the nVidia forums...

If any got this and better yet, can share a solution, it would really help. I guess those who are really affected are the ones using Vista with an 8xxx card.