First some general definitions:
Copyright is protection of "works of authorship" from being copied. The U.S. Copyright Office has an extensive site. It includes a primer on Copyright Basics (PDF).
A trademark is either a phrase or logo which identifies the maker of a product or service. The primary purpose of trademark is to allow customers to recognize a distinct brand from others. Thus, it is illegal to use a trademarked phrase or logo which could confuse customers into thinking that your product is from that other company.
The U.S. Patent and Trademark Office also has a site which includes a primer on Basic Facts on Trademarks. However, this is a bit dense and is mostly concerned with registration fees rather than usage. The legal firm of Beck & Tysver has a site on intellectual property BitLaw which is more useful.
Other resources include gamasutra.com and the Stanford Library Site.
Game systems are different in many ways from other media such as books, music, and movies. Most importantly, games rely heavily on ideas like how to move around a piece on a playing board. New games constantly take the ideas of old games: like ways of rolling dice, or ways of moving pieces on a board, etc. Ideas cannot be copyrighted, this is explicitly emphasized in the U.S. Copyright Offices' form letter (form FL108) with instructions for copyrighting games. Games can in theory be patented, but this is a difficult process. The only non-computer game patent I know of is for methods used in the Magic: The Gathering card game, held by Wizards of the Coast.
In regards to role-playing and board games, there are a few points which I would emphasize. Please go to the sites above for any specifics.
|^ Up to Games&Copyright||Ahead to New Games >|