I just built a new system and have no problems with vista. I was very concerned about it before the build but decided to go with it anyway. I have had virtually no problems running AHII at max settings. I do have an occasional stutter due to my hard drive choice but that is rare and doesn't cause any issues. It is really only when I approach a furball and (6K or dot range) then it is done and I have no more problems.
EVGA 780i (PCIe 2.0) MB, 4 GB Corsair Memory, Intel E8500 3.16 Ghz C2D, MSI 8800GTS OC 512 MB, WD 500 GB harddrive(7200 rpm AAKS5000), Samsung Syncmaster 2253bw, Antec P182 case.