To export an mp3 file from Audacity you need the file libmp3lame.so. One way of getting this file is to install the packages liblame0 and liblame-dev from the Mulitverse repository.
When you first export an mp3 file Audacity will prompt you for the location of the file libmp3lame.so. The file should be in the folder /usr/lib
(This short note applies to Ubuntu 6.10 and Audacity 1.2.4.)
