I'm running Ultimate 32 bit with the 8800GTX. I installed the latest driver for the card last week and all seems to be good. One wrinkle however, when I restart the computer out of sleep mode more often than not I will get a blank, black screen on my monitor. Not a biggy, I just turn off the monitor and turn it on again and everything is fine. This never happens while running apps just startup from sleep. I read the driver notes and it is a known defect. Hopefully to be fixed on the next update.
But other than that it seems great to me.
Hope this is a help.