New Vista Hotfix for Multi-GPU Setups

"Those of you who run run Windows Vista with SLI or CrossFire setups should download this hotfix. The KB945149 hotfix resolves an issue that, in some cases, could cause systems with multiple graphics cards to "perform more poorly than expected" in both games and benchmarks. Microsoft describes the issue as such: "A graphics processing unit (GPU) or part of a GPU link may incur a small scheduling latency on a new Direct Memory Access (DMA) packet. This is true if the DMA packet is submitted to the GPU that has previously run out of work and if another GPU in the linked configuration is very busy. In some scenarios, significant
starvation of one or more GPUs in the linked configuration reduces the expected performance of an application. The hotfix may resolve the problem, but it isn't freely downloadable. Instead, users must visit this page and submit a request to Microsoft's Online Customer Services. The company also warns, "if you are not severely affected by this problem, we recommend that you wait for the next service pack that contains this hotfix."

you need to ask for the hotfix its not for every one you need to submit your request here
http://support.microsoft.com/kb/945149