See my last post. I installed a new graphics card. I considered replacing the psu, but determined it was unnecessary. That case is pretty cramped and not really designed to be worked on.
The 6450 is pretty slow, so for $150 you can do considerably better. I'd try to get a 6870 or 560. Watch for sales. For example, right now Newegg has a 560 for less than $150 with mail in rebate.http://www.newegg.com/Product/Product.aspx?Item=N82E16814500225