Whatever you get, WoW is going to look fine. It's not that graphic intensive compared to like every other new game out and the hardware now can handle it no problem. I don't recommend basing your build around that game.
I agree with Puddle_Jumper, theres no real reason to get Raid 0. I did it with my Raptor X's when I first got them and honestly, I don't even remember the difference. I'm sure if you looked at some benchmarks, you would see a difference but is a second or two really worth the money and risk? 7200.11 drives are plenty fast.
With the OS thing, I say get Vista. I have been using it for a long time now and I have no trouble with it. In my opinion, I think it is finally a solid OS. Plus you get DX10.