New video card for a Dell Dimension E-510?

I want to upgrade my video card so that I can play games like 'World of Tanks' and 'Battle field Play 4 free', at decent graphics settings with good frame rates. I've already upgraded to a 500 watt power supply I think, and a friend gave me a 'NVIDIA GeForce 7300 SE/7200 GS' video card which did get my gaming performance up a bit. So i want to further upgrade my video card and I can only spend below $200. Here is my computer documentation >.http://support.dell.com/support/edocs/systems/dim5150/en/sm/specs1.htm>. Thanks for any help. God bless.|||AMD HD 6870. You can get one from newegg.com for less than $200, the best card for that budget.