Would it be safe to assume duplicates would have the same file name and/or size/properties? If so you can use a standard duplicate finder application, such as Duplicate File Finder (freeware). On the other hand, if duplicates could have different file properties you'll need something more advanced, particularly if they're recorded and not downloaded/ripped songs since there would likely be no tags attached.
Let us know.
Here is a "hypothetical" question for you. Say for instance I have a 10k song library of MP3's. Now my friend has a song library of 22k songs. Is there a program that would assist me in finding which songs are duplicates and which ones are not. Am I stuck going track to track.