Yes that card will run Diablo 3 and WoW, obviously not on max settings. This tough, is a downgrade from the 9800 gt so what I recommend is you find another 9800 gt. Alternatively you can go to the next level of video cards and get a radeon 6850 for 60 bucks more, thus allowing you to enjoy the graphic detail more.
Thank you Carlosb for taking the time to read and respond, it is appreciated!
As I move to the Radeon 6850 or beyond, am I going to reach a point in which the far outdated components of my current PC limit the card I should be purchasing? If I buy a GTX 680, am I going to see the same performance out of it that someone with an up to date PC would see?