So, if you want to be on the safe side.

New hardware, go vista 64-bit. Old hardware, go XP pro 64 bit. In a nutshell. (Note: This is in no way the absolute truth, but does in general count as truth.)

I'm very happy with Vista myself. Good performance and very stable.

I am EXTREMELY annoyed, seeing as I bought Vista Ultimate, 8G of RAM, and a quad-core, yet I still run 20 fps on my main when quad-boxing.

Is there something I am doing wrong? My system specs are:

Intel(R) Core(TM)2 Quad CPU Q6700 @ 2.66GHz 2.67 GHz | 8.00 GB of RAM | Vista Ultimate.

Also, I have (2x) NVIDIA GeForce 8800 GTX.
What video settings do you run your wow instances with (mainly: maxfps and maxfpsBK, view distance, resolution.)

Also, how many dirs do you play wow from, and do you know if you run wow on a seperate harddisk (physically) or not?

Thirdly, any idea if you use CPU core assignment or not?