Yeah, that 3850 that hsetir recommended would do it. Of course it wouldn't live up to it's potential since it would be held back a bit by your CPU. Anyway this powercolor 3850 AGP is a little cheaperhttp://www.newegg.com/Product/Product.aspx?Item=N82E16814131090
but you have to make sure that your PSU can run it properly. If you don't have a unit of over 400W with at least 18A on the 12v rail (though you may squeak by with dual 14A 12v rails) then you are going to probably need to upgrade your PSU. If you don't you risk damaging your system. Anyway if a game requires a minimum of a Geforce 7900 GTX or X ATI Radeon 1900 XT I can't imagine that your CPU would meet the requirements.