help with checking for a duplicate name in db

I am using mysql to store information for a personals program I'm writing (that's how I'm teaching myself PHP) I've come to an impasse, though. I need to be able to check and see if a username already exists, so they are always kept unique. Here is my code I'm trying use, but am not getting it to work. I've tried it about 10 diferent variations of this code...but i'm ready for help now! I know I shouldn't be using the db as root, but I'm planning on changing that way before I release this. Thanks for any ideas! working script: http://www.politics2004.com/personals source: http://www.politics2004.com/personals/register.phps