*SIGH*
This is one of those threads I get so annoyed by. He says he doesn't have money and just wants to play today's games, and the first thing somebody does is suggest 2 7800GTXs in SLI! Thats just pitiful!
The bare minimum for today's games is an ATI Radeon 9600XT. Anything lower than that and newer games become sort of a struggle. Stay away from the GeForce FX or especially the GeForce MX cards. If you don't mind spending a little more for a decent card, get the 6600GT, which can run all of today's games on near-full blast settings on 1024x768. It would be the best card for your money if you can afford it. Under your circumstances, I wouldn't suggest going higher than the 6600GT, unless you just lied to us about money being an issue.