Due to licensing restrictions, Digital Performer does not have built-in .mp3 export functionality. To enable .mp3 export from DP, visit this website to download LAME Framework version 3.97, then unzip the downloaded file and place it in Macintosh HD/Library/Frameworks/. If DP is already open, quit and re-open DP and you will now be able to export .mp3's! For DP8, please see this Tech Note.