I just listened to a podcast called Rules for the Revolution produced by Collette Vogel, episode 11.  She reminds me of every boy’s dream: mannerisms of a cheerleeder, intellegence of an attorney, (which she is) and the tenacity of an activist.  Her guest was Tony Falzone, head of the Stanford Fair Use Project.  Fair use refers to exceptions in copyright law.  Falzone was eloquent in his explaination of the topic, and divided the issue into 4 factors.  The first factor to consider when deciding to use another’s work in your own is: did you change it?  The courts often look at wether or not the finished product has been transformed, and to what degree.  The second factor is: where did the original material come from?  If it is an historical record, or not copyrighted material, then end of story, its free to use.  The third factor to consider is: the amount of original material that you are using.  If you made a short film, and used the first 20 minutes of the soundtrack to The Little Mermaid, you would be in violation of copyright law.  And even if you only use a little bit of the soundtrack to that film, it had better not be the part that sings, “under the sea” – its most recognizeable lyric.  That is called by Falzone as the “heart of the material” (he actually used a scenario that cited the review of a book in which the review was a ’spoiler’).  The fourth factor has to do with the effect on the market that the new material has.  If sales of the original are threatened by the new material, then don’t do it.  You will be sued.  Most of the factors are matters of opinion to an extent, so be careful either way.