Please help w/building a new gaming machine

Hey soldiers,

I often find myself looking through the forums for help when I am desperate, well today is different. My brother needs a new computer and we have time and a little bit of cash. He almost spent $1650 on a ral piece of crap form his local computer store until I found out and showed him the parts were less than a grand on the net (newegg, tigerdirect etc). Anyways he wants to spend around the $1500 range and I think we can do that and get him a kickass gaming machine. Here is what I'm thinking, please critique my build and if you see anything that deconflicts i.e. mobo and cpu etc bring it up so I dont make a huge mistake. I am very into computers, have made numerous upgrades to mty past comps but never fully assembled one.

Case: Xion Dazl gaming tower w/420watt psu
Mobo: ASUS Striker extreme nForce 680i SLI w 7.1 onboard sound
CPU: Intel Core 2 Quad Q6600 (4x2.4 gHz/8mb Cache/1066 FSB
RAM: 2048MB 1066 DDR2 PC2 8500
Gfx Card: eVGA GeForce 8800 GTS 640MB PCI express SLi supported
HD: Western Digital 10,000 RPM 150 GB
Sound Card: SB Audigy X-Fi extreme gamer
Network card: Intel pro 10/100/1000
op system: Windows XP home

Please critique this build and give me any tips you might have. Also is Newegg, and tiger direct the best place for prices? thanks.

Zach Kirby