The author of this program, Philippe Laval, says You are looking for an application to encode your sound files in MP3, DropMP3 is done for you.. The program runs on MacOS, uses the LAME encoder, and is released under the GPL. Note that the web page is more or less duplicated in English and French.

Version 1.0.6 is shipping as of March, 2003.

http://philippe.laval.free.fr/DropMP3/US/DropMP3_US.html