Well - I'd not go under 512 for sure, but that goes for most anything today - especially with cheap RAM prices. 1 Gig. ram is what I'd recommend.
The graphic card isn't all that important, I used a GeForce 4 Ti4200 (128 MB) to run the game for a significant portion of time, and while loadsequences lagged and took some time, once loaded (into my 1gig RAM) it ran decent enough. Loading in MC and IF was a drag.
I then changed to an ATI 9800XT (256MB), and it seriously improved my load times, but again - once loaded the differences were marginal, although I now ran with more options enabled.
For WoW I'd say RAM is likely one of the most important ressources once the other specs are "average"
(nice and vauge, huh?)