(Edited from a post by eleutheromaniac)
An idea is not protected by copyright; copyright protects only the unique and original presentation of that idea once produced in a tangible or recordable form.
"Anytime that you create a creative, copyrightable work and it is fixed on a tangible medium (ie, paper, videotape, etc...) it is copyrighted. You don't have to register the work to have copyright protection, although registration brings other benefits such as the immediate right to sue and potential statutory damages, notwithstanding actual damages. So in sum, once you create it, it is copyright protected
." - FindLaw for Legal Professionals | Law & Legal Information
Fair Usage or Theft (Mike C)
Copyright term and Public Domain.
Note: Just because something is considered public domain shouldn't give one the right to pillage it at will without giving some due credit to the original source. Call it 'Writer's Etiquette'.
U.S. Copyright Office
UK Copyright law
Austrialian Copyright law
PS - You can make the copyright symbol by holding down alt
and then typing 0169
on the number pad.