i cannot find a software to convert ac3 to mp3 or wave under the mac OS9 formatt. What can i use and where can i find it?. I'm chopping up some dvd footage and making quicktime files.

Unfortunately, for OS9 i'm not sure, however for OS X, you can use wiretap to record anything soundwise that is playing on your computer (including audio from the dvd player app).

Remember to only use it for personal or educational use, otherwise grab the respective copyright holders' permission first.