In unix, to rip the audio out of most basic movie
files (including mpg and avi)
to mp3:
mplayer -dumpaudio file.mpg
mv stream.dump output.mp3
The first command runs mplayer and dumps the audio to a stream file
in the local directory (stream.dump)
The second command moves (renames) it to an mp3.
Sorry, but I don't know how to do it in Windows.
Same way. :) There's a Windows port that works quite well (I've been
using it for a while now while my desktop is trapped on Win2K).