Here are some links that will help answer copyright questions that you might have.
Copyright Slider-Using a handy red arrow you can slide from "Before 1923" through "Published after 2002", use your mouse to see what copyright laws apply to the work you are considering for use. Much of the time you may get a "Maybe" response, so be sure to let your mouse hover over the red answers for clarification.
Copyright and Fair Use Guidelines for Teachers-A handy chart summarizing copyright do's and dont's.
Copyright and Fair Use for Educators-A thorough (5 pages) explanation of the nature of copyright and fair use principles as it applies to educators. It also has a good description of the limitations and proportions that can be used under Fair Use guidelines.
Copyright in the Classroom-This site, sponsored by the Copyright Alliance Education Foundation, offers free classroom resources and ideas for integrating instuction about copyright into your everyday lessons.