In my application, I want to copy a song from iPod Library.
How can I do that?
Yes. It is possible, but hardly practical, to access raw song data. What you do from there is up to you. Here is a lengthy and detailed description of the process: http://www.subfurther.com/blog/?p=1103.
EDIT: Please be aware of App Store guideline 9.1 before making use of this technique. These guidelines require a developer login, so I've removed them from my post.