305W is fine for low end GPUs.
That pentium is serious bottleneck. Also I'm fairly sure your motherboard only has a pcie1.0 slot which causes more problems.
Basically, you need a new computer. Any video card that will be compatible will, at best, barely play games. Unless he's playing older games, what games is he playing?
To run the latest games at playable settings (bf3,WoW,Mass effect,skyrim,etc) a $500 custom built pc is about as cheap as you can go. Cheaper than that is hard unless you can reuse parts (or go with really budget parts). $1200 is about where the law of diminishing returns really kicks in.
If you're interested, I can put together an easy build list. I need to know the following:
-What parts are still working in his dead computer? (i need links or model numbers preferably) If you don't know what is broken just list all the parts and explain the "brokeness".
-What games does he play and at what resolution?
-Country (or favourite parts website)