Pixelpipelines matter a lot. A geforce 7950 GTX is the best you cna get, Or a 1800 ATI. 7300 is like a low budget card, a 7900 is a one of the best. Whats your budget?
And ram is just how much ram is on the GPU, nothing more.
Main Rig: I7 920 CPU, 6 Gigs ram 5870 GPU
M17X Laptop 2.8 Ghz Dual Core, 4870 Radeon