iTunes is the best app to convert your aiff file to mp3 format. You can do it in Peak, but you can’t save as much information in the file.
Open iTunes and drag your mix file into the iTunes music window. iTunes will copy your file into its database. The image below shows my “Kothman 1a mix” copied into iTunes.
Next, use the Get Info command ([CMD ] – I, or from the File menu). Fill in the title, your name as the artist and the composer, year, and genre as shown.
Once you click OK, your iTunes listing should update to reflect the changes.
Open your iTunes preferences and check your Import Settings.
Choose mp3, and Higher Quality, 192 kbps setting.
Back in the music library, with your project selected, choose Create MP3 Version from the Advanced menu.
You will end up with two versions of your project in the music listing. If you view the bit rate, you should see the difference. The mp3 version should be the second listing. You now need to copy the mp3 version into your project folder. You can find it by using the Show in Finder command from the File menu.
It will open a finder window with your mp3 file selected. Copy that file to your project folder.
With all of this done, you can turn in your project folder to my drop box using the instructions previously posted.