If you are using intensive 3D utilities, I'd say go for 2gig. Either do it with 4x512 or 2x1GB, your choice.
look up the specs for your mobo and see what the highest RAM it can use is, then buy that. ANything higher will be restricted to the mobos max RAM rating, anything lower will be slowingyour programs down.
Not bad, but there is better out there. A better graphics card can help your 3D performance as well.