Which graphics card is best for my pc?

my pc config. i3 processor, 4gb ram, 512mb ati radeon 4350 vga card.. but i cant run some games like GTA 4, cod blackops, even conviction also i'm getting some problems.. so my friend has sparkle 1GB 8400GS vga card(nvidia).. he offering me to buy that with low price than he bought coz his bought another card for him.. so whats my question is.. is it better for me to buy that card.. coz i need to play my fav games like cod, ac2, ac brotherhood and mostly GTA4.. so kindly reply me that card can play GTA4 or what card i need to buy.. cheap but best... i'm frm hyderabad.. so i also want to know price.. thank u for advance