option to buy another graphics card please

[fregg]

First sorry for my English I speak Spanish, my question is this, a fast 512 graphics card is enough to play at 1600x900 dolphin is my question because I do not know much about graphics cards and are very expensive, I recommend that graphics card which is not very high price.
The Dolphin PC buying guide and I saw it but the graphics card lowest price, you could buy is no longer sold in my country, this graphics card is expired
below the specifications of my pc
a phenom 2 945 at stock 3.0
4 gb of ram ddr2
1600x900 lcd monitor
650W power