Was not allowed to add to the discussion on the wiki so I am posting here. The: http://www.zen-cart.com/wiki/index.p...Custom_Sidebox page give great info. One minor issue is that it tells you to create two sideboxes within that sample code without explaining and caused me to scratch my head for a minute.

remove this line of code: require($template->get_template_dir($column_box_default, DIR_WS_TEMPLATE,
$current_page_base,'common') . '/' . $column_box_default);

And you will achieve what you were probably trying to do, create a custom sidebox.