I want to buy nvidia graphic card?

want new nvidia 512 mb ddr2 with H/w TnL vertex shader 2.0 and pixel shader supports 3d range betwwen 2k-3k INR .I have p4 2.4 Ghz with 1gb ddr2 ram intel 945g chipset i dont know much about Graphics card .i want to play 3d games of avg sys req.please help thank you