I've ran wow on my old p4 Dell with integrated graphics at ~17fps with everything at its lowest detail at 1280x1024. Lets just say it was playable questing, nothing else. Perfectly fine if you've just started playing the game, but once you start to raid/5 man you'll definately need a rig with a graphics card.
Depends on how well you want to play it. I could probably run WOW off a Nintendo DS but that doesn't mean I'd like to. Off most integrated graphics you could run it on low settings with a low resolution but if you're wanting great visuals,performance and no lag during raids you'll be in need of a decent dedicated graphics card.