I'm sorry, actually, i had some misinformation. Anyways, Since your just doing video editing, which is pre-rendered, almost all of the processing will be done by your CPU, so, if you want to increase performance, you'll want a beefy CPU vs a beefy GPU. Which makes a lot of sense, sorry for the confusion, and just for the sake of conversation, the Quattro line of cards cost so much more because they are aimed at professional use, 3D rendering, CAD, ect. However, i'm not completely sure how you get your video, but you might want to read up on HDCP, ether way, any Gforce 8 series and up support HDCP, so you probably want to go that route. On that, your going to want a lot of memory (ram) the more the better, but 2gb will fine 4gb would be awesome. For video cards, your not doing anything graphically intensive at all really, so you can just pick up an 8500gt and have no problems, in turn saving you some money, as they are cheap.
What is HDCP? - A Word Definition From the Webopedia Computer Dictionary
What is HDCP (high definition copy protocol)?