Think you could check on this and offer advice?

I've been fiddling around with different components for a while, and i think that this setup works fine with me, except for a few burning questions that im dying to know. First of all, xp or vista, and secondly, is the 780i worth the extra 100 or so dollars when i've heard nothing but good about the 680i (even that it's better for overclocking)? I know that the case i've selected isen't the best for oc'ing, but im going to probably stick a few more fans an all that stuff in there. My last question is whether i should go 9800gx2 or 8800 gtx. I know that the gx2 is more powerful, but im probibly going to want to add another card in a few years, and the 750w psu definatly cant handle 2 gx2's. And by the way, does modifying the coponents and adding new ones and maby modding the case affect the warrenty?

Here's my future (hopefully) rig. If there's any problems, i would love too know and i know that i dont have a moniter, mouse, keybored, speakers etc selected. Im splitting this with someone and they agreed to buy all that stuff. Now that i'm finished with my shpeal, here ya go.


Case: Digital Storm 450Si (Black Aluminum Edition)
Power Supply: 750W Corsair HX (Dual SLI Compatible) (Silent Edition)
Processor: Intel Core 2 Quad Q6600 2.4GHz (1066MHz FSB) (8MB Cache)
Motherboard: nVidia 780i Core 2 Quad (nForce 780i SLI)
Memory: 2GB DDR2 Corsair at 800MHz XMS2
Floppy / Card: - No Thanks
Hard Drive 1: 320GB Western Digital (16MB Cache) (7200 RPM) (SATA)
Hard Drive 2: - No Thanks
Raid Option: - No Thanks
Hard Drive 3: - No Thanks
Optical Drive 1: DVD±R/RW/CD-R/RW (DVD Writer 20x / CD-Writer 48x)
Optical Drive 2: - No Thanks
Network Card: Linksys Wireless-N 300Mbps (Supports 802.11n/g/b)
Video Card: nVidia GeForce 9800GX2 1GB
TV Tuner: - No Thanks
Sound Card: Creative Sound Blaster Audigy SE
Physics Card: - No Thanks
Cooling: Air Cooled Stage 3 WindTunnel (Copper Heatpipe Heatsink & Zalman Case Fans)
Case Lighting: Blizzard Internal Lighting (Blue Edition) (Cold Cathode Tubes)
Round Cables: - No Thanks
User Manual: Personalized Platinum Digital Storm Binder (Includes Paperwork/Benchmarks/CDs/Manuals)
Overclock Processor: Yes, Overclock the processor as much as possible with complete stability
Overclock Video Card: Yes, Overclock the video card(s) as much as possible with complete stability
Overclock Memory: Yes, Overclock memory timings (Includes Corsair Dominator Airflow Fan Upgrade)
Tweak Windows: - No Thanks, Please do not tweak the services on the operating system
Windows OS: Microsoft Windows XP Media Center 2005 (Includes Service Pack 2)
Restore Kit: Digital Storm Specialized Recovery System (DVD Image Based)
Protection: - No Thanks
Office: - No Thanks
Benchmarking: - No Thanks
Pre-Install Game: - No Thanks
LCD Display: - No Thanks
Surge Shield: - No Thanks
Speakers: - No Thanks
Keyboard: - No Thanks
Mouse: - No Thanks
Warranty: 3 Year Platinum Care Extended Parts & Labor Warranty
Support: Lifetime Toll-Free Platinum Care Technical Support