I have the same problem except mine does it at random. You know, right in the middle of writing a CD-R, or in the middle of browsing the "net", or for no reason at all.
I guess this is a "feature" of the new drivers.
[rant]I'm about done with NVidia. When's the last time they released WHQL certified drivers? Every new driver is just a different set of problems. I keep upgrading to "fix" problems and all I do is trade them for new ones. 3dfx might be a little behind the times but I wouldn't have to put up with this crap. As soon as the Voodoo5-6000 comes out, I'm all over it.[/rant]