I have the free evaluation version of 4, the same as Blinn, and it well worth having a play with imho - as Blinn mentioned the real time movement and things are really impressive and there are lots of very good video tutorials. I'm currently leaning animation basics in Maya but having played around in Motionbuilder a little I think that's where I am going to go for the next stage of things. I'd definitely recommend trying it out, it has some excellent features.