I know there are javascripts, and possibly php scripts, that you can implement into a form ( like when someone fills info into a form and submits it), that will either alert the user that a word is banned, or will automatically replace the word with another word. I would suggest doing a search for something like "javascript bad word filter", "php bad word filter", etc., or similair. Also, there are several sites which offer free scripts, such as
www.hotscripts.com. I'd suggest looking there first.