To rebuild the menu in Drupal 6 you have to go to admin/build/modules. In drupal 5 the menu is cached in the cache_menu table, so it is easy to invoke a menu-rebuild by emptying the table with a simple mysql command like TRUNCATE cache_menu;. (I have a handy script that empties all tables starting with cache_). However in drupal 6, to get a module's hook_menu() re-invoked, you have to rebuild the menu by going to admin/build/modules. You do not need to submit the form. Going to that page with appropriate permissions is sufficient to invoke a menu-rebuild.