The reason is that they have huge issues with their high end cards. SLi in the first distro used to bluescreen Vista, and so did any G71 and G80 cards. The support is getting better, much better, but I am still not convinced that its fully wonderful. Until SP1 I still don't plan to actually go to vista on ithor of my computers.
Cheers
Cameron
Simviation Forums
Flight Simulator and other chat
