The Q6600 would be perfect for the video editing, much better than a dual-core CPU.
Does 1920x1080i mean you need a monitor with a width of 1920 pixels? Those come in 24" sizes or more, and they're still expensive. A monitor like that does need an 8800 GTX for some of the more demanding games.
That memory sounds like a great deal. Nice price, great brand. I suppose you need to find a friend to order half of it to actually get rebates on both pairs of sticks, but I'm not sure. Maybe find something that comes in 2GB sticks, to allow upgrading to 8 GB later? It depends on the motherboard, of course.
My PC includes a Q6600, BFG Geforce 8800GTX OC2, PC Power & Cooling S75QB 750W Silencer, GA-P35C-DS3R. It works really nicely. You could get the GA-P35-DS3R and save $30 over the P35C. The Silencer is the best 750W PSU in the world as far as I know. Look at www.anandtech.com in the PSU section, great reviews there. Highly recommended, especially if you plan to add lots of TV tuners and hard disks.
About the motherboard - one thing I really like about the GA-P35C-DS3R is that it allows a 8800 GTX and 3 PCI cards to be used at the same time. I don't know of others that can do that. For example some Asus models have the PCI slots too close to the PCI-E 16x and the video card blocks a PCI slot. You may not have a modem or an X-Fi but you will have TV tuners, I guess. When I install the TV tuner I'll actually have all 3 PCI slots in use.
I'm guessing that the video editing will require tons of hard disk space. The PC P&C has enough connectors for 4 SATA hard disks and a SATA DVD-RW. I think it can handle more if I buy some splitters but I'll worry about that next year.