OK: Vista SP2, 32 bit.
I installed the latest 195.55 Vista drivers fresh from nvidia, and SLI was successfully enabled after a reboot. I also disabled Physx. Ran Lightsmark 2008 and the SLI performance was good. I didn't notice any artifacts or anything strange, and there was definitely nothing like the white flashing screen.
I didn't check what SLI profile for Lightsmark 2008 was set to. It used to be AFR1.
Not sure if there's a nvidia-bug-report or similar I could generate in windows? I, err, don't spend a lot of time there....
Anyways, holler if there's anything I can provide.
ws