Using 84.21 on my 6800GT here, no probs at all aside from a couple masking issues in Final Fantasy XI.
Ding! Those are one of the ones I downloaded, so maybe those are the ones I was so happy with.
Make sure you clean ot all traces of the old drivers before installing any new ones. Safe Mode and driver cleaner seem to do it for me
I don't normally bother, since Nvidia drivers are "supposed" to be fully removed with XP, but that's precisely what I had in mind to do this time, as I'm convinced that two drivers have become intertwined here somewhere.