Old PC, new graphics card

Hello everyone,

I have an HP Pavilion a6643pt desktop: 

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01600752&tmp_task=prodinfoCategory&cc=us&dlc=en&lc=en&product=3824147

 I am starting to feel some issues playing some games on this computer.

I want to solve this problem by buying a new graphics card for my computer.

http://www.amazon.co.uk/Nvidia-GeForce-DirectCU-GDDR5-Graphics/dp/B00DBPKEOI/ref=sr_1_1?s=computers&ie=UTF8&qid=1399315393&sr=1-1

This seems like a good option, though i have no idea if it runs on my PC. If someone could clarify that for me it would be much appreciated.

Thank you very much in advance.