Many people ask questions about using copyrighted content. There is a US law called Fair Use that allows for the use of copyrighted material under certain conditions. Parody, news and a transformative work are just a few. There is a very good video on YouTube. I can't post links yet but you can find it if you do a search for "A Fair(y) Use Tale". I hope this answeres some questions about copyright.
It's actually a lot more complicated than you make it sound. It's not just whether you are using a work in a parody, etc., but whether you are using the work commercially, and how much of the work you are using. Here is the US copyright office information: http://www.copyright.gov/fls/fl102.html There is more good information at EFF: http://w2.eff.org/IP/eff_fair_use_faq.php and Stanford University: http://fairuse.stanford.edu/