I was also having problems with my 7900gt. Everytime I came out of sleep mode the screen would get all scrambled. Reinstalled microsft drivers and all is well. Havent tried to run any games yet though.
there is definitly something up with the power modes and nvidia drivers. Im just happy the microsoft drivers are working right now.
When you say power-modes, do you mean that cpu-throttling causes graphics distortions and a hard lockup? If so I have an open bug you should validate and comment on. It's been open for a few months now so I really hope you're on connect.