If you can afford the faster machine with more VRAM, buy it. If you can't, buy the less expensive model. I've done video editing with my 2.0GHz Core Duo (NOT Core 2 Duo) MBP with great results-though a bit of a wait for the DVD to be created.
If you're going to do a lot of serious video editing, I don't think the MBP is the best platform for the job-the Mac Pro is a much better fit for that. But if you're going to get an MBP, get what you can afford and you'll be happy.