The DMCA (Digital Millennium Copyright Act) actually has very detailed information for web site owners on what to do, how to do it, and how to determine if the complaint is real.
It also protects web site owners in the case of actual copyright infringement, provided you follow the directions...
Wikipedia has good information on the DMCA at:
Digital Millennium Copyright Act - Wikipedia, the free encyclopedia
And here is the actual text of the DMCA
http://www.copyright.gov/legislation/dmca.pdf