If you aren't going to overclock it, then the Athlon will bottleneck the HD 6950 rather significantly in some games.That's not to say that the Athlon isn't up to the task.You just need to push it a little bit (3.2 ghz should be enough).
Power supply wattage doesn't really matter much.If it's a high quality unit it's good enough.
This is pretty much the best "budget" (<50$) power supply you can buy right now. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
It has enough power for your system even if its overclocked with added voltage.