I am messing around with drivers right now trying to find some stable ones for my 8800 GTS 640 (Vista 64bit) I have tried 171.37 but whenever I try to enable SLI, it asks me to restart my computer. Okay, fine, great, do what please Nvidia. After restarting, SLI is still turned off and when I try to enable it, same thing again. I tried updating to 174.74 but after a while in games I get a weird full-screen black flickering that crashes the PC (no error screen, just freeze). It does it for the XP drivers as well as the 64bit Vista. If anyone can help me out, I'd really appreciate it!