Auto load classes by class name like Zend Framework

How can I auto load my framework controllers and models by their class name like the Zend Framework does?

Zend Framework auto loads classes like so:

new Application_Controller_Index();

meaning that controller class is located at application/controllers/IndexController.php

Why not to have a look in the source code ? http://framework.zend.com/svn/framework/standard/trunk/library/Zend/Loader.php

just in case, probably the simplest way:

spl_autoload_register(function($classname){
    include str_replace('_', DIRECTORY_SEPARATOR, $classname) . '.php';
});