I need help from graphics card guru's

Ok I'll keep this short sweet and to the point.

I'm a sailor, I know very little to nothing about purchasing a decent rig to run my games on and I'd like some advice from you graphics card gurus!

I've got my eye on an HP Pavillion Elite 5200t ATX, I'm wanting to get it with all these goodies:
-64bit Windows Vista
-Intel Core 2 Quad processor Q9400 [2.66GHz]
-4GB DDR2-800MHz dual channel SDRAM
-500GB 7200 rpm SATA 3Gb/s hard drive
-768MB NVIDIA GeForce 9600GS

All that plus mouse, keyboard, monitor and speakers will run me about $959, however, for an extra 100 bucks I can get a 1GB NVIDIA GeForce 9800GT or for an extra 120 I can get a 1GB ATI Radeon HD 4850.

Can I get away with the 768MB 9600GS or should I bite a bullet and go for one of those 1GB cards? And if I should, which one?

Thanks!


..and crap I just now noticed I tossed this in the wrong forum...