Hello Lizzie,
Welcome to DaniWeb.
I use a program called Amadeous II that was developed by hairerSoft.com It is shareware, and I think it cost $40 or so. But what it allows me to do is input audio from the microphone, or from the mic jacks in the back of the computer. I do not have a USB / Firewire camera to test things on, so I am not sure Amadeous will work strictly with that interface.
BUT, if y ou have an audio out on your camera, you might be able to:
* Wire the output jack of the camera to the mic in jack on the computer
* tell your software to record
* tell your camera to play
* walk away
You may need to adjust your input levels on the computer, so that you do not over-drive the software. Amadeous will allow you to do that.
I realize this might not be the "firewire-only" solution, but it should get the job done for you.
BTW, is it possible to shut OFF the video feed using iMovie? I remember using Adobe Premiere, and I could kill the video feed, so that only audio was captured and processed.
Christian