128 MB Graphics card or 512 MB RAM?

I have a P4 3.0 GHz computer with an Intel motherboard and 512 MB DDR RAM. What is a better upgrade option out of a new 128 MB Graphics card (like 6600GT) or an extra 512 MB RAM? I use the computer for 3D gaming and running softwares like 3D Studio Max, Photoshop etc.
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