To begin with, could someone please explain to me how important RAM is within a graphics card, and how exactly it works? Does a 512Mb card in a computer with 512Mb standard RAM basically just mean the computer has access to 1024Mb when using a graphics intensive programme, or does it matter that the memory is within the card? Likewise, many ready-made computer offers include statements like "512Mb graphics card (64Mb onboard, the rest shared.)" Does that mean that the card only actually has 64Mb of RAM and draws the rest from the computer's standard RAM?
Finally, aside from how much RAM they include, how much difference is there in the various graphics cards available, and how will that difference be noticeable? I want a gaming machine that will be as high-powered as possible without costing too much (just like everyone else), and if I have, say, a GeForce 7600GS as opposed to a 7300GS in an otherwise identicle build is it going to strongly affect the games I play?
I'm no computer-whiz and I need information in laymen's terms. Any help will be greatly appreciated, thankyou.