You graphics card really isn't that bad. Few games should be taxing it too terribly hard, including GTA3.
You would almost assuredly notice a far larger gain in your gaming experience by getting a stick of 256DDR than by upgrading your card, and for far less money at that.
There isn't a game that comes out, and that includes the tiny ones that no one hears about, that I do not own. And I can play every one of them at 1024x768 resolution, max details, on my GeForce2 GTS. That includes GTA3 which, coincidentally enough I just picked up again to try to get 100% completeness this time around.
But, if you really want to get a new video card, wait about 6 weeks and buy a Radeon 9700 if you have the money, or 9500 if you don't have $200 to blow. ATI is coming out with 2 new cards shortly, which will drive down the price of the 9700 and 9500 about $50-$100 less than they are now.
The only problem with that would be that ATI doesn't play GTA3 very well. I guess because it's a port optimized for hte PS2 which I believe uses a nVidia based chip.
You could wait until the new nVidia chip comes out and then pick up a 4600 for probably in the neighborhood of $200 or so wholesale.
I'd still recommend more RAM though. That will help out your experience in GTA3 a lot, as the problem is that you can't cache enough of the city in memory to play it well enough. It's a huge system memory hog. much more so than video memory. My old GeForce2 can run it so well because I run it with 512MB of RAM.
