Bad words filter for username registration

Im pretty new to php and mysql and sooner or later im going to come across the problem of new registrants signing up and using offensive words as part of there username,,, (im not at all bothered about them using them in their password fields as they are not seen)...
Well i've fell off the end of the internet trying to find something or a tutorial on how i can go about this, (all i seem to be finding is chatroom and shoutbox related) does anybody have any ideas that can point me in the right direction..thanks for your time..MJ

I would recommend regular expressions. Here (http://1212jtraceur.memebot.com/user_scripts/cleanlanguage.user.js) is a user script that I use to filter language from what I view. Let me know if you need help modifying it, although I know very little about php and mysql. (Linked file contains profanity)

Thanks 1212jtraceur
Thats exactley the kind of thing im looking for and to be honest the words that are in it are the only words i would put in anyway..now how do i add that to my user registration, would i have to create a linked table in MySQL or just add another columnand username is already my primary key, would this have to change?