I just found out from looking at YouTube videos that the toy can only go forwards and turn left. No right turns and no reverse. I suppose that makes for an unpredicable and fun toy, but I have a feeling it's not going to work that well for a robot..
So I'm thinking of using DC motors to control his tank treads after all, and use the IR for his mimics only (voice + head and hand gestures). That gives me a lot more control over his movement, while still getting a wide range of typical Wall-E mimics "for free". Sounds good!
As for acquiring a Wall-E, I missed out on one that was sold on Ebay for just $35 this morning (by oversleeping). I'm now tracking two others in the same price range, hoping to get one within the next few days. So hopefully within two weeks time the fun begins :)