I got the 8800 GT and the same proccessor and 2 gig ram as MDGreengenes. I can run 4 WoW's smooth on it, aslong as i stay out of cities. It needs to load a few minutes untill it get's pretty smooth with 20 fps and some laggspikes in the 4 major cities.

I'm not a pro, but if you'd get the 8800 GT you're good.