I did the switch from an X1900 XTX to a 8800 GTS. I unistalled all drivers from Nvidia and ATI through control panel, then rebooted in safe mode and uninstalled all Nvidia and ATI drivers with Driver cleaner and rebooted. I reinstalled my Nvidia chipset drivers then rebooted, and last I installed my Nvidia Forceware 97.02 drivers, and rebooted.
All of my graphics performance is just fine in games and on benchmarks. I get no errors or crashes.