The WoW client is universal binary, right? I only played it on my PC laptop (~20fps @ 1024x768, low detail) a while back; would be interesting to see how it runs on more recent hardware.
Im running Vista SP1 and its more stable than on my old PC.. You just have to make sure that you install bootcamp... install vista then install the 2.1 update... Then update to service pack 1 within vista (Something like that).... thats if you want to use vista.
There are lots of walkthrough guides on the internet everywhere just google them plenty to choose from.
Sounds alot, but once I have it I will have a damn good read, I am tempted to put Windows XP on a 20GB parition on my Macbook. I assume XP is much easier?