Re: 400$ build
looks like a good build.
b1gapl beat me to the "why not use a brisbane?" point.
Also, for $20 more you could move the HD up to 250gb, if your friend thinks he'll need more space.
Also, if you have a Fry's near you...or a Micro Center, or similar, I'd buy the case there. $16 in shipping for a case? annoying as crap.
Antec 300 Illusion
430w Antec Earthwatts
AMD Q4 640 Propus
2x4gb Patriot DDR3 1333
750gb Seagate 7200.11 Hard Drive