A good place to read up on video cards is at
http://graphics.tomshardware.com/graphic/index.html Here they test all of the new cards on the same system to see how they compair.
Useing this chart
http://graphics.tomshardware.com/graphic/20031229/vga-charts-03.html you can see how some of the newer cards run "Unreal Tourn 2003"
Next you can check pricesat
http://www.pricewatch.com/. What your going to find ...in most cases... is that the little bit more that you can pay to go with the 256 meg ver of a card over the 128 meg ver, is about the same money to bump you up into the next/ better ver of that brand of card.
One other thing you can pick up by going thru these boards is that less people have trouble with Nividia based cards than the ATI based cards. I'm not saying one is better than the other, all I'm saying is I read about more pople having trouble with ATI and aces high. I run a GeForce 64 meg card on a 2 gig CPU and run in the 50's for FR.
There are alot of choices and a lot of info to go thru when it comes to video.