The IntranetJournal has a listing of all of the parts in their "Creating a PHP-Based Content Management System" series:

• Part 1 of the series begins with a look at the overall plan for the CMS, and a look at PHP and the concept of object-oriented programming.
• Part 2 takes a look at the basic PHP code that will power the CMS.
• Part 3 examines the creation of the database and the database connector.
• Part 4 explores validation, and the creation of a validator class and the creation of sections for the content that needs to be managed.
• Part 5 introduces security to the content management system, and shows how to create a system that is accessible only to those with authorization to access it. It also takes a look at creating a log-in for users.
• Part 6 discusses layouts for the content, templating systems, and talks about possible add-ons and features that can enhance your PHP-based content management system.

All of these parts provide everything you'll need to learn how to roll your own CMS - source code, explainations, and plenty of examples to go around. It's a little older (written in 2004 with PHP4), and there might be a better/easier way to do some of the things now (like the use of $_POST instead of $HTTP_POST_VARS), but the basic concept is there.

Thanks to PHP Magazine for the pointer...