This addon provides a simple way of changing themes in your osCommerce store. You can switch to a new theme for the season or to spruce up your store, or just to test out a new look. Just upload your new theme package and then select your new theme in your store's Admin.
Instructions are included for using the ThemeRoller tool to download stock themes and design new ones. It includes a method that allows you to design WYSIWYG on your own store pages.
Forum support thread: http://forums.oscommerce.com/topic/367934-addon-theme-switcher/