Okay this is a little complicated but I just figured it out today but its nothing new. Doing this gives you access to all the music files people add using the audio application on facebook regardless of if thier your friend or not.
1. Add The Audio application from the menu on the left (Click applications>browse more applications>audio... not that hard but some kids are stupid)
2. Once in the application click everyone’s audio and search for what song you want
3. Click on the song that takes you to a page that you can listen to the song or add it to your profile
4. View Page source and scroll down till you see something like this picture
5. Download the linked file from its source for free!