I'm quickly running out of space on my HD. Part of the problem is every increasing amounts of video of my daughter. I'd like to get a good-sized external FW drive to hold it. Now, if I'm working with iMovie, can I run the footage off the external HD, or should I put it on the internal HD? That is, from a performance perspective? Also, I assume it's best to render the final project to the internal HD, and burn the DVD from there, but is it possible to do it straight from the external HD? Anything to look for in an HD other than FW capability?