simple iMovie question

I normally use final cut, and I know that program is at a totally different level, but:

I'm trying to teach a buddy how to use iMovie and I want to know if there's a way to change the disk on which clips are captured. It looks like all you can do is capture on the system drive.

Seems like a really bad idea...anyone know how you can change this or if there's a way around it, if that is in fact a limitation?

thanks in advance for the brain power.

beautiful...thanks a lot.