@MrNase: what would be best is to filter the username the same way it is filtered when the usual registration process occurs, because for now, it's not deleting spaces and illegal characters... anyway, this is the only thing i think to enhance... (would add a error like: your username contain illegal characters, etc...)

may be a good thing to add when users can posts when as guests (where we can add a username, the script would verify if you have a known username, and if yes, display the password field to berify...) anyway, i'm highly into enhancements... lol