I want to upgrade my HP Pavilion a 720n to play games on it...I want to know the best compatiable video card.?

I Believe that your Motherboard only has an AGP slot not the newer PCI-Express, Therefor you will have to go with an AGP graphics card. Depending on ur budget I would recommend the Nvidia Geforce 7800GS 512mb which u can get for around �70, Also please remember that you will have to upgrade your ram i would suggest having at least 2GIG