Watch the video, "Remix Culture" from the Center for Social Media: http://s3.amazonaws.com/videos-flat/remix_culture/remix_culture.m4v
After you view the video, use the "Code of Best Practices in Fair Use for Online Video" to help you understand fair use rights and mashups, remixes, and other uses of protected works.
Another useful tool for the filmmakers among you is "Yes, You Can!" by Peter Jaszi for The Center for Social Media.
We all know that illegal file sharing is, well, illegal. It is also unethical. Maintaining academic integrity, avoiding plagiarism, and giving credit where credit is due are all ethical decisions we make as participants in the academic community. While there are many debates regarding copyright term limits, fair use, etc., it is generally accepted that artists should be free to make use of their works as they wish, whether that is to share their work freely or to attempt to make a living from the sale of those works. The blog Trichordist: Artists for an Ethical Internet provides plenty of opinion on why you (and the people you know) might want to pay for the songs (and other media) you download: http://thetrichordist.wordpress.com/
Other questions? Ask a librarian!