said by FizzyMyNizzy:
I know you guys are recommending him a low-end card for a good reason. I only check the list OP is getting is correct.
It sounds like to me his son works, and or save up money. A lot of thing could happen to that pc. New cpu, new monitor etc., in the future.
If OP is under the assumption he needs to replace his PSU, and thus his case also, to upgrade to a discrete GPU, he may be mistaken, depending on GPU (and he does NOT need the 7950, son's research aside, based on his given requirements).
I don't know how old his son is, how much money he makes, or how well he knows computers. What I do know is that he is looking to play L4D2 at higher framerates on his current rig.
Based on his given requirements, he would be best served by purchasing a low-end GPU like the Radeon 6670/7750, or GeForce GT 640.
There is no need to upgrade everything about the computer to do this, and definitely no need to go with a GPU like the Radeon 7950. If I may dip into the forbidden realm of analogies for a second, that's like going from a Fiat to a Dodge Challenger or Chevy Camaro when all they really need is a Chevy Cruze. Don't assume the customer knows the relative power of the car they are asking for. ("Hi, I just need a car that gets better than 30 mpg to commute 20 miles round trip every day"--not a prospective Challenger/Camaro owner).--
If we lose this freedom of ours, history will record with the greatest astonishment, those who had the most to lose, did the least to prevent its happening.