Please check my build

First time getting a custom PC. Please check my build.

My questions are:
Is this a big enough power supply?
Ram: I only need 2 GB which one?
my video card will be either the Nvidia 8600 256 or 512 not sure yet. I may SLI in future but doubt it.
I don't think I'll over clock anything.

Here it is. 111930(shown or) 111933 same config except vid card.

Specifications:
Case: Digital Storm Twister LITE (Black Aluminum Edition)
Power Supply: 520W Corsair HX (Dual SLI Compatible) (Silent Edition)
Processor: AMD Athlon X2 6000+ 3.0GHz (Dual Core) (2 MB Cache)
w/HyperTransport
Motherboard: Asus M2N-E SLI (nForce 5 series SLI Chipset)
Memory: 2GB DDR2 Corsair at 800MHz Dominator (Dual Channel)
(High-Performance)
Floppy / Card: - No Thanks
Hard Drive 1: 400GB 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)
(LightScribe Edition)
Optical Drive 2: DVD-ROM/CD-ROM (DVD Reader 16x / CD Reader 40x)
Network Card: High Speed Network Port (Supports High-Speed Cable / DSL
/ Network Connections)
Video Card: nVidia GeForce 8600GT 256MB (By: eVGA) (PCI-Express)
TV Tuner: ATI TV Wonder 650 (HDTV, Video Recording, FM Radio, Video
Input and Capture)
Sound Card: Motherboard Multi-Channel High Definition Audio (7.1
Channel)
Physics Card: - No Thanks
Cooling: Air Cooled Stage 2 (Silent Artic Cooling Heat-sink (Copper
Heatpipes)
Case Lighting: Blizzard Internal Lighting (Blue Edition) (Cold Cathode
Tubes)
Round Cables: Enhanced Interior Air Flow (Optical Drive & Floppy Cables
(Blue Edition)
User Manual: Personalized Platinum Digital Storm Binder (Includes
Paperwork/Benchmarks/CDs/Manuals)
Overclock Processor: - No Thanks, Please do not overclock my processor
Overclock Video Card: - No Thanks, Please do not overclock my video
card(s)
Overclock Memory: - No Thanks, Please do not overclock my memory
Tweak Windows: - No Thanks, Please do not tweak the services on the
operating system
Windows OS: Microsoft Windows Vista Home Premium
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: Microsoft Multimedia Desktop 2.0 (Multimedia Keyboard +
Optical Wheel Mouse)
Mouse: - No Thanks my keyboard comes with a mouse
Warranty: 3 Year Platinum Care Extended Parts & Labor Warranty
Support: Lifetime Toll-Free Platinum Care Technical Support

Just out of curiosity, what is the difference between the Dominator ram and XMS2. It has the same specs and all.

The ATI Radeon HD3850 isn't listed in the drop menu. And does it perform better than the 256 or 512?

Thanks,