A few days ago I was having problems getting my models autoloaded by Zend Framewok, after a little research I found the solution.

For this project I am using Zend_Application and Zend_Application_Bootstrap_Bootstrap for bootstraping my application. Enabling autoloading is as simple as adding this line to application.ini:

appnamespace = "Application"

or you could add a $_appNamespace property to your bootstrap class:

class Bootstrap extends Zend_Application_Bootstrap_Bootstrap
    protected $_appNamespace = 'Application';

After enabling this namespace some mappings will be created that will allow Zend Framework to autoload your classes correctly. This is a list of the folders the class names prefix and where Zend Framework wil attempt to find that class

If your class starts with Zend Framework expects to find it in
Application_Form application/forms/
Application_Model application/models/
Application_Model_DbTable application/models/DbTable
Application_Model_Mapper application/models/mappers/
Application_Plugin application/plugins/
Application_Service application/services/
Zend_View_Helper application/views/helpers/
Application_View_Filter application/views/filters/
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