Login to Joomla! 1.5 Site Administrator panel (http://www.domain.com/administrator).

1. Mouse over Extensions in the main horizontal menu, then click on Plugin Manager.

   

2. Locate plugin named System - Legacy, and then click on the check box in front of it.
3. Click on Enable button.

   

4. Ensure that Legacy: 1.0 status appears on the top right corner, and the Enabled column for “System - Legacy” is ticked. The Legacy Mode has been enabled.

   

With Legacy Mode, users can now use extensions, modules, plugins and templates from Joomla! 1.0.x series in Joomla! 1.5 and ensure that the modules are working properly. Joomla! 1.5 now is compatible with Joomla! 1.0.

Note that if you don’t install and populate Joomla! with sample data when installing Joomla!, the default modules and plugins are not loaded into the Site Administrator Panel. If you cannot find the Legacy Module plugin, try to build the sample data again.