It is perfectly legal to put forward with making a site that has information pertaining to a copyrighted material. To have images, origional manuscripts, or any thing in specific that is copyrighted on the sight without permission is illegal.
Put simply: A forum such as this isn't breaking any laws, because its just a site where people talk about pokemon. If you were able to D/L images, games, shows, etc. owned by Nintendo, then it would be illegal. Your sight, other then ideas expressed on the sight, would have to contain images, text bodies, and the like that are origional. Basically don't put up pictures that have a copyright by nintendo, Don't put up official scripts of shows, and don't allow D/Ling of shows, music, or games owned by Nintendo.