Copyright infringement is not a pleasant topic. Some self-publishing authors find themselves in trouble without even knowing it, by doing something as innocent as including the lyrics from their favorite songs in their book.
Music is one of the most protected copyrightable works; infringement of copyright can carry heavy fines for which the author is responsible. If you are going to use the lyrics from a song in your book, you will need to have permission from the original copyright holder. This includes cases where you are only using a stanza or two and sometimes even if you are using anything more than a single line.
Only song lyrics created and first published prior to 1923 are in the Public Domain in the United States. If the song was created after that, you will need permission to use it (or parts of it) in your work.
There are two great resources on the Internet for finding the rights holders for most music and song lyrics, from the two leading music entities, ASCAP and BMI, respectively:
http://www.ascap.com/ace/search.cfm?mode=search
http://www.bmi.com/licensing
Self Publishing Advisor 