Seeking assistance for first gaming build

I am building my first system.. It will be built mostly for MMOs (WoW, Operation 7, Combat Arms, Rappelz, Aion), video editing (Sony Vegas 8.0) image editing (Adobe Photoshop). I am seeking help for various parts in my build. I am buying my processor from my local MicroCenter because I don't want to take the risk in it getting here DOA from shipping or mistreatment, plus its cheaper. I am working with a $396 budget atm to get the rest of my parts. I don't mnd ordering from newegg as long as its not my processor. My monitor resolution is 1600x900 (VGA) but I most likely will buy a DVI to VGA adapter. I am putting a (?) behind the parts I am most unsure about. I am most unsure about the video card due to the worry if it'd fit in my CM Storm Scout Mid Tower (Leaning towards ATI over Nvidia). I welcome opinions, words of advice and understanding for a firstime builder. Thank you

SPECS:
Case: CM Storm Scout Mid Tower with 700 PSU (Already Bought from Newegg) http://www.newegg.com/Product/Prod [...] -_-Product
Motherboard: Foxconn Inferno Katana GTI LGA 1156 Intel P55 ATX Intel Motherboard (already bought from Newegg.) http://www.newegg.com/Product/Prod [...] 6813186175
Processor i3 530 ($86 at MC, $114 at Newegg) or i5 760 ($169 at MC, 209 at Newegg) (?)
RAM: 2GB or 4GB DDR3 1333 SDRAM (?)
Primary HDD: 500 GB or 1TB (?)
Secondary HDD : 80 GB SATA (Already installed in case)
Video Card: HD4670/HD5750/HD5770 (open to any other suggestions here, most confused with this part, case supports cards upto 10.5 inches long) (?)
Operating System: Windows7 64x Home Premium http://www.newegg.com/Product/Prod [...] -_-Product

Video editing is the only thing there really pushing you in any direction with regard to ATI / nVidia where nVidia's CUDA support is helpful. If you're adding Adobe Creative Suite to the mix, there's more CUDA support benefits there.

At 1600 res, the cards you listed will work, but if moving to 1920 x 1080 is in your future, I'd go for a 5850 or 460 SC. At 1600 res, Id grab a 5750/5770 or GTS 450