The easiest method would be to use Audio Hijack. (
http://www.rogueamoeba.com/audiohijackpro/ ) . It will allow you to record the audio output of the Mac and then you can use QuickTime to reencode as whatever format you desire.
There's several applications that do this. Do a search at VersionTracker (
www.versiontracker.com ) and you'll find others.
-Geoff Miller
MadCow Studios