I have a 2,1 macbook with 4GB ram of which 64mb are dedicated to the video card. Can I increase this to at least 512?
Generally, VRAM is soldered on/in somewhere. I suppose you could, if you had the know how, but the short answer is, no.
Edit: That is, VRAM is not (usually) taken from the pool of "available RAM," it's actually separate RAM entirely. And dedicated to the GPU, only.