The RAM will help overall performance, but probably not the problem you have.
Since you only have PCI slots, you are topped out as far as what card you can get. You'd have to replace your motherboard to get a better card... and if you're going to do that, you might as well replace the whole system.
If you don't feel like you could build, buy a pre-built one (check here before you buy, of course) and pop in a decent graphics card.
But, try the RAM first and see what it does for you.