In a rather enlightening episode of Everything Is a Remix, host Kirby Ferguson explains the concept of Fair Use and legality of this doctrine. He also offers three provocative questions to ask yourself before using copyrighted material.
I recommend using this three-step test. For each clip you want to use. Number one: Is the clip you are using illustrating a point? …Number two: Is this point clear to the average viewer? And lastly number three: Did you use only the amount that was reasonably appropriate to make your point? …if you can answer yes to all three you have a strong case for Fair Use.