you better get 1 G RAM.
My gaming experience with 512 is kind of cacat something.
After pumped to 1 G, wow!

PCI-Express

I second Bogardan comment.

LinkZ, your setup is about same as my.
And you don't need to setup everything to MAX.
That will cost you a bomb, likely 5k+ PC.

For me, the improvement from 512 M -> 1 G is especially when I crossing zone, no more pc-lagging.
pc-lagging still occured, but far lesser and very short.

The next important performance for the online gaming is your connectivity.

good luck, have fun

Brother, what do you really want?
setup a PC that's no lag? Supercomputer?

Put it simple, min 1G RAM will not make you pissed.