Then I realized I was making it much too hard. The answer is actually quite simple. As long as you don’t mind having a folder called “iMovie events” at the root of whatever hard drive you move the video to.

There are two things to note in following these directions. You have to use the iMovie interface so it knows where to keep track of the files (and as noted, iMovie creates its own folder). Two, while the instructions keep saying “external firewire drive,” any physically separate drive mechanism should do. I haven’t tried it with USB, but I have used a separate internal drive on my G5.