I 5-boxed on a dual core (first gen, not core 2 duo) 2Ghz laptop with 4 GB ram and a 256MB nvidia 7600 (mobile).

I had everything on low and I had stable 20-30FPS on my main and 10max on my slaves.

worked fine all through burning crusade. I know that there are some new shaders etc but you don't have to use them.