Nvidia has released a beta version 158.42 Vista driver for GeForce 8800-series graphics cards. The driver is available for both Windows Vista x86 and Windows Vista x64. Nvidia claims this driver adds support for SLI multi-GPU technology in DirectX 10 applications, improves both single-card and SLI performance, and brings compatibility fixes in numerous applications.

http://www.nvidia.com/object/winvista_x86_158.42.html
http://www.nvidia.com/object/winvista_x64_158.42.html