After reading through Tweaktown's Cat 8.3 article it seems that the drivers work great in Vista but are dogs in XP:
ATI Catalyst 8.3 Analysis - XP & Vista :: TweakTown
Miso seems to have used Vista for this quick rundown just like I will do with the actual review. IMO, he will see a performance DROP with the 8.2 drivers which I have already experienced in Crysis and WiC.