Gaming Computer build 600~

The Spinpoint F3 should be fine for gaming. It is pretty much the standard drive everyone uses now in their budget gaming rigs. His mobo doesn't even look like it supports SATA 6GB.

The StealthXStream 2 did very well in this review from HardwareSecrets, I don't know about the original StealthXStream listed though.
http://www.hardwaresecrets.com/art [...] eview/1058
http://www.microcenter.com/single_ [...] id=0334768

Newegg has some deals on Quality PSUs right now. You can get a 650 Earthwatts for <$50 after rebate.
Antec Earthwatts 650 - $63 after code DECAN10 - $48AR
http://www.newegg.com/Product/Prod [...] 6817371015

from my reaserch the bigger the cache on your hard drive the better it is for gamming. I went more cche and have no issues. As for mobo not soporting sata 6gb of ram. Board is fine.
As for the Power supply there are 2 opinions. go cheap and take a chance or spend more for reliabilety and a great warrenty to back it up. I built a system for a freinds brother. money was the issue. save 25$ on his Power supply and 3 moths later it shorted out and took Mobo and Video card with it. now it just cost him 500$ to get new parts for it. You ask him is 25$ cheaper was worth it

twistter, there are other good power supplies outside of Corsair. Just check the review of that StealthXStream 2 I posted above. It basically could have been rated as 80 Bronze and also reached about a 700 watt max in their overdraw test. While that isn't recommended use it more than reaches the advertised 600 and also at a very good efficiency.

As long as you do your homework you can find plenty of quality PSUs without paying big $$ or only staying with one brand.

Yeah, he had the original StealthXStream in the OP, which is older/cheaper. I linked the StealthXStream 2 in my first reply as one he could go with through microcenter.

Given the current options I would go with the Earthwatts 650 right now as well. I agree about the mobo, the ASRock 770 Extreme3 is another good option in the $75 range as well.

A HD5870 is stronger than a HD6870; if the price is the same, since you'll be covered for power, get the HD5870 unless you need some feature the HD6870 provides.. I wouldn't buy a GTX470 unless I absolutely needed CUDA / PhysX, as it runs hot and sucks power.
A free mobo sounds nice, unless it's really obsolete, like limited to 1000MT/s or some such like the 6150 boards.