There are many video cards to choose from and they're not all from Nvidia....ATI has a very healthy selection of cards as well. The big questions are:
1.) what does the rest of your PC look like spec-wise? No point in suggesting you a card only to have the rest of your system hold it back. Please post a dxdiag so we can see the rest of your specs:
Start - Run (if Vista or Win 7, the search box acts like Run) - type dxdiag - hit Enter - "save all info" button - open txt file and copy/paste EVERYTHING here
Picture of process: http://www.windowsresource.net/cimages/gotodxdiag.jpg
2.) What power supply do you currently have in your PC. Depending on what the dxdiag will show, we may be able to figure it out, but if not....you will have to open your case up to view the specification sticker on the power supply.
3. Budget. State how much you're willing to spend. If in another country other than the States, indicate your currency and hwat country.
1. Specs are:
operating system: Vista Home Premium (6.0, Build 6002)
system manufacturer: Gateway
System model: DX4820
Bios: System Default Bios
Processor: Intel Core 2 Quad CPU Q8300 @ 2.5GHz (4CPU's), ~2.5GHz
Memory: 8156MB Ram
Page File: 1104MB used, 15261 available
Direct X version: DirectX 10
2. Power supply is 500W
3. Budget is anything within reason, at least up to 300-400.