There seems to be a Problem with the new 81.84 and 81.85 Nvidiadrivers and SH3. I've got the very same Problem with my 6600 GT and the 81.85 set.
http://www.subsim.com/phpBB/viewtopic.php?t=44475
No remedy at the moment with this driverset AFAIK. You can only downgrade to 7x.xx-something Drivers, wich could prove difficult with other games and an 7er Series NVidia-Card. It seems like it's NVidias fault.
NVidia's Driversets are a royal pain in the.. well, you know.
EDIT:
Issue fixed in 81.87 Beta, grab them here:
http://www.nzone.com/object/nzone_do...etadriver.html
(by fixed I mean listed in the Release Notes as fixed, don't have time ATM to test it personally)
A little Warning: this drivers are beta and certainly not WHQL-certified. (wich usually doesn't do squat anyhow)
So they may or may not blow up your computer or eat your dog. Use at own risk.