Auction Software - PHPAuction

Okay nbew issue just arose. I posted in phpauction forums a week ago, and no hits. Anyway, if a user registers a name with an apostophe, the software adds slashes. okay, good. Now i find that more often than not with the username, the slashes are not stripped.

Here is the issue. If said user posts an auction, the listing is set to user 0 and the listing loads with a string of errors and no seller information. I can go into mysql and change the user id number and it loads fine.

What I am looking to do is just make certain characters "illegal" in the usernames so they cannot submit when registering unless they do not have certain characters such as ' " + = ( ) $ % and the like. Any help with this would be greatly appreciated. I am holding off on a couple deals that should up my usership significantly until I figure this out, and I am pretty much a php rookie (at best).