djangoringo :
Nvidia cards are better for that, 8GB of ram is fine, you can always bump the ram for 16GB if you need.
This ram has a combo with 670 gtx evga or 660 ti asus : http://pcpartpicker.com/part/gskill-memory-f312800cl10d16gbxl
I strongly disagree with the RAM comment here. In a video editing machine, the amount of RAM is nearly as important as the CPU. You want enough RAM to be able to store the entire video file you're working on (as well as revisions) in system memory, and they can get considerably larger than 8gb,
especially since you want to edit HD video. 16gb is the minimum I would put in a new video editing machine at this budget.
Don't buy RAM seperately for this machine. RAM from two seperate kits is fine for a gaming machine, but when you're working on a project, you want
stability, which is better when all RAM is from the same kit.
The latency of the RAM in also more important to a video editing machine than it is to a gaming machine. Getting a 16gb set of CAS 8 RAM is worth the extra ~$15 over CAS9 for editing.
for video editing, it's best to buy all your RAM at once, in a single kit.
http://www.build-my-home-computer.com/build-video-editing-computer.html
enjoy!