The 600 watt power supply is at or near the minimum for that video card. If you under power the system you will have continued problems. I would keep a watchful eye out for a 900 watt if you can.
I HIGHLY recommend a aftermarket heatsink/fan set-up if your brother is going to be gaming at all. It will make a big difference with chip performance and overheating protection. They are relatively inexpensive. I think I paid $36 for mine. I would also HIGHLY recommend using the heat paste. The paste that comes with the AMD chips is not great and if you don't have a good seal your chip could go bye bye.
I would not get a HD under 1 TB, space is cheap. Here is one for $59:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136534
Same comments in regards to the RAM.
Most motherboards come with all the cables you need. You can check the specs which should tell you what it is boxed with.
"The people should not be afraid of its government, the government should be afraid of its people." V
