Always Always Always get permission before you use any music in a film which was created by someone else....

Just do it.....

There are more than enough starving artists out there, new bands, solo musicians that are wanting to have their music in films to satisfy any request you have for music to worry about locking up your film in court over the use of a song or part of a song....

There is a listing of artists willing to let you use their music here http://www.digitalcinemapictures.com/info/composer.htm

There is also music available for very very low cost at Creative Commons as well as at MagnaTune (recommended)

The following is an excerpt about Music Sampling and the law
"There is no fixed amount of permitted usage that is set forth in the fair use statute and the cases do not define any fixed amount of usage.  For those who continue to believe in the absolutely false and incorrect belief that there is any fixed amount of usage that will be acceptable under the fair use doctrine (read the numerous articles on my site dealing with fair use but especially "Fair Use: Further, Further Issues."  Click on "Articles for Writers and Publishers"), a case from the Sixth Circuit should give you nightmares."

Ivan Hoffman is an entertainment law, Internet law, publishing, copyright and trademark attorney, practicing for over 32 years.  His web site, http://www.ivanhoffman.com has won *8* prestigious web site awards.  You may reach him on the Internet at ivan@ivanhoffman.com.  Ivan Hoffman is not affiliated in any way with our company or our web site or otherwise with us.  All of Mr. Hoffman's articles are based on United States law.