For HD video editing it all comes down to CPU and RAM. If your serious about the editing, Id go with the i7 instead of the i5. (Please make sure the Socket Type for your CPU matches the socket type of the Motherboard. I know a few who have encountered this simple mistake.) Your motherboard of choice is epic. Can't go wrong with HDD's any more, but if you want to squeez out as much performance as possible, I'd look into Wester Digital's new storage density technology
http://www.youtube.com/watch?v=ij3bR0fRq48&feature=channel_video_title. RAM is all dependent upon what type of editing your into and what software your using. 8GB is usually perfectly fine, but you'll always have room to upgrade to more if needed. Video Card all depends upon what you are wanting to play. Ensure your PSU is able to adequately sustain power not only for intense processing tasks, but also for future hardware upgrades. If you want a clean legit computer, look into something like the SILVERSTONE ST1500 1500W Modular Power supply
http://www.newegg.com/Product/Product.aspx?Item=N82E16817256054. It will keep your setup clean of unnecessary cables by allowing you to only attach the cables you need. The only downside is its very pricey.