If you love having the latest drivers but feel sketchy about installing non-WHQL certified ones, Nvidia has released a “WHQL Candidate” set for the 169.21 series. For both Vista and Windows XP including 64-bit versions, you can download them here
. These aren't technically beta drivers, and do promise compatibility fixes among other things.
They also add support for the recently released 8800 GTS, so if you happen to have one of those cards you'll probably want to grab it.