There is a lot of info on the web what a good system for video editing system should be. It depends mostly on how much do you want to spend :-)
I have a 2600K CPU with the DZ68BC and the GPU inside is very good. Not good enough for the latest 3D games, but you might find it good enough for video editing.
An Intel DZ68DB with a non-K i5 or i7 CPU may be a good option. If your not in a hurry, then you can even wait for Ivy Bridge CPUs + boards (expected in April 2012). The new embedded GPU is announced to be much faster and has improved video transcoding.
Be aware that that some CPUs have a HD 2000 (6 executing units) GPU and others a faster HD 3000 (12 executing units) GPU inside.
As already mentioned it depends on what you can afford. As video editing is very processor intensive, if you get the best you can afford then it'll be longer before you need to replace it or upgrade (although I'd stay away from the very top spec items as they attract a significant price premium). If it was me, I'd probably wait for the Ivybridge boards to appear as already mentioned. You may find a backup, format and reinstall (or backup and system reinstall from a factory recovery DVD if you have one) will give your old PC a new lease of life to keep you going until then.
I have spent a lot of time doing video editing myself and my biggest piece of advice is to get the highest performing storage subsystem that you can afford. Video editing can be *very* I/O bound. I thus highly recommend that you look at a Z68-based solution. This chipset supports Intel(R) Smart Response Technology, which allows you to utilize a fast SSD as a cache for a single drive or (better) RAID array, significantly improving I/O performance...
Oh, and BTW, you missed the DZ68ZV, our newest Z68-based desktop board...