If you are not prepared to spend too much on a graphics card, then the Powercolor AX6870-2GBD5-6DG is an excellent solution for you. It has 2GB of memory and open-ended software support. The card also has a powerful ATI Radeon HD 6870 that will be able to run most games without any lag and can be used to enhance the overall performance of your computer.
In addition, the card is certified by Windows and ensures that it will be able to work perfectly with this operating system. However, if you do not have a good case to put the graphics card in, then the cooling system will be a problem that you will have to deal with.