Thank you all for your input

. And yes I am aware that my Athlon II X2 isn't ideal for gaming. I just bought this computer expecting to be making some upgrades so I am ready to put the money into it to get at least a quad core CPU. I think that from all the input above that I will be going with the 5770. I'm not too concerned about super high res and framerate, I just want to play the games I have at atleast medium graphics with an acceptable framerate.
Thank you all again, I did't expect to get this many replies.
And by the way, this is my first "gaming computer". I've been an XBox gamer for the longest. I got tired of paying $50 a year for Live service.