since you're somewhat budget constrained, scale back your mobo, video card, and hard drive.
the asus p5n32-e sli ($195) will OC almost as well as the striker and save you $100. (the q6600 should hit 3.2ghz fairly easily.)
save another $200 by getting an 8800gt/512mb. it's in spitting distance of the 8800gtx in most benchmarks. unless you're running at 1920x1200 or higher, the 8800gt will run crysis just as well as a gtx.
lastly, save another $100 and get a 750gb drive. this western digital ($160) is faster than the seagate and almost matches the hitachi 7k series 1tb.
that's $400 saved so you can afford another 8800gt if you want to outperform a gtx ultra.
one caveat though. don't expect any nvidia 680i based motherboard to be fully compatible with the new 45nm penryn quad cores (q9000 series). so this build will probably deadend with the q6000 series. if you want penryn compatibility and don't need sli, then look for a mobo based on the intel p35, q35, or x38 chipsets.
retail vista is more expensive ($320) than the system builder version ($170). vista options
asus striker review: http://www.xbitlabs.com/articles/mainboards/display/asus-striker-extreme.html
8800gt/gtx benchmarks: http://www.xbitlabs.com/articles/video/display/leadtek-8800gt-extreme_11.html#sect0
My names nick and id like you guys to look at my proposed setup. this is not final yet and the most i can spend is prolly 1500 maby 2000 but my parnts prolly wont go for that. currently i am buying my parts at www.newegg.com except for my GPU im goin with tiger direct for that seeing as it is $70 cheaper and comes with Crysis. well here it is:
1. Mobo: Asus Striker Extreme
2. CPU: Intel core 2 Quad Q6600. $ restraint wont permit me to buy the core 2 extreme QX9650
3. GPU: EVGA GeForce 8800 GTX
4. HDD: Seagate Barracuda 7200 1TB of storage.
5. RAM: Corsair XMS2 2GB
6. Case: Antec nine-hundred
7. OS: Microsoft Windows Vista Ultimate
P.S. Do i need to get the Windows Vista Ultimate System Builders pack? it costs $200 more
thank you for looking over my post.