Please post your budget.
Since the machines psu won't handle high end graphics card you will be getting a midrange graphics card(in order to fit into your budget). Probably an 8600 or a 3650. Also I checked and does your machine still have the 512mb of ram and the celeron? Heres a better page for reference on your pc.
http://www.e4me.com/products/products.html?prod=T3516