Since intellectual properties, such as copyrights, are so involved and controversial, I've decided to pass along some websites that other persons have passed to me or that I've found:
U.S. Copyright Office
Direct Legal's Copyright Guide
Brad Templeton's Guide to Copyright
Plagiarism Today: Main Site
Plagiarism Today on: Fan Art and Derivative Works
Hopefully, these websites can help you avoid headaches in the future, whether you are making original art or - dundundun! - making art or writing work that is based off another existing piece!
Also, take good notes on the differences between copyrights, trademarks, and patents. You would think it's simple, but it isn't! This stuff gets pretty confusing, and people aren't 100% protected, of course. But, like I said, hopefully all you guys and gals out there can arm yourselves with knowledge.