You need QT Pro to do it ($29 at
but it's easy.
To save the video portion alone:
1) Open the movie in QT Player
2) File >> Export
3) In the dialog window, give your export a name (different from the current movie name).
4) Select Export: Movie to QuickTime Movie
5) Click on "Options..."
6) Choose your Video settings, and un-check "Sound".
7) Click OK. Then click Save in the main dialog window.
To save the audio portion alone:
Steps 1 & 2 the same.
3) In the dialog window, select Export: Sound to AIFF (the name will auto-change to "yourmoviename.aif"

4) Click on "Options..."
5) Select your Compressor and other options (some Compressors have an additional Options... button).
6) Click OK. Then click Save in the main dialog window.
Easy as pie. Good luck.