I'll add another "pro" comment for the Mac. I know you said that you wouldn't use it for internet access (for video only). If you have a wireless network (easy to add if you don't) accessing the web with a Mac laptop could not be easier. The only thing you have to do is turn it on. No configuring at all. We (OK, my wife) have 2 PC laptops. I, unfortunately, am tech support in our house. While not difficult, it can be time consuming (for me anyway) to set up a new computer and get it on the network.
When I brought the PowerBook home, I turned it on and BAM! Web surfing in minutes. And, as some one else said, they are more secure from virus attacks than PCs.
And, as I said before, iMovie and iDVD are included with the Mac as is iPhoto, iTunes and something called Garage Band that allows you to compose original musical scores for your movies. Personally, I have not used the Garage Band software as it is newer than my PowerBook. Now, if you need to make more sophisticated movies, Apple has what I believe is the industry standard professional editing software - FinalCut Pro. They also have a version of FinalCut that falls somewhere in between iMovie and FinalCut Pro. So, as your skills needs develop, the software is available to grow with you.
Once again, I am not a diehard Mac person. I am typing this on my PC, which is what I use everyday at home. And I have edited video on both platforms. For what you want to do, go with the Mac. You will not be disappointed.