I never liked maya.
Anyway, for one get more RAM and a 64-bit OS. You may also have alot of background services you don't need that are hogging your RAM. I would also suggest you upgrade your CPU if you're doing alot of 3d modeling. Saying you have a 512mb nVidia card doesn't really tell us much, since there are many different models, so I don't know if that is limiting you as well.