Increasing video memory on an older macbook 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.