Need recommendation: good user management system (PHP/MySQL)

I'm just starting to learn PHP and it's going to take a while before I can create a really good script to password protect a section of my site, with a good admin control center to manage my user's accounts. Therefore I'm asking for recommendations on a good retail script that can handle this for me until I'm skilled enough to create my own. I'm a little desperate since I'm using a poorly written CGI script at the moment. I'm looking for a customizable PHP/MySQL script to password protect an area of my site and add/edit user's accounts. You know the usual member management script. Thanks in advance! // Andreas