Hi, I'm looking to upgrade to a new computer and if I can figure things out well enough hopefully build it myself, at least partially. One of the biggest questions I have had for a long time regards graphics cards, which I must admit I know almost nothing about.
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.

RAM on graphics card is entirely separate to actual computer memory and is exclusive to the card.

Many branded computers use onboard graphics which use a chunk of the system's main memory. So basically if you have a computer with 512Mb of memory and "64Mb shared", that basically means Windows will only tell you it's got 448Mb of memory. The rest is being used by the graphics on the board. You can usually alter this in the BIOS, but onboard graphics are a cheap and cheerful solution and no good at all for anything gaming-wise beyond Spider Solitaire.

As to the difference between the cards, you get what you pay for. If you pay peanuts, the games will probably run, but you wouldn't be able to crank them up to the top settings as the card wouldn't cope. As to which one you get, it depends what games you're going to be playing.

Upgrading to a better video card will let you play many games on high setting. The Integrated card wont let you play much games on your computer. Is the GeForce 7600 GS any good? Im upgrading my other computer and I wanted to upgrade to the better Video Card before Neverwinter Nights 2 come out.

Just go Dedicated. Its Pwns.

I would go for an nvidia 7600gt and no lower. The 7600gs is a slower version of the gt. The GT is noticably faster and is the overall better price to performance ratio.

I also wouldnt go all out on a $400 + video card with directx10 coming out soon.