New products tab.
Files:

1. include/modules/new_products.php
2. includes/templates/YOUR_TEMPLATE/templates/tpl_modules_whats_new.php

Special products tab.
Files:

1. include/modules/special_index.php
2. includes/templates/YOUR_TEMPLATE/templates/tpl_modules_special_default.php

Featured products tab.
Files:

1. include/modules/featured_products.php
2. includes/templates/YOUR_TEMPLATE/templates/tpl_modules_featured_products.php

Check that are listed only active products (files under module directory).

For more details contact Zen Cart Website Design