If the pages `www.yoursite.com/special`, `www.yoursite.com/special/anotherpage`, etc are the actual paths to the content and not aliases, then `page--special.tpl.php` should work for all of them.  If, however, they are aliases to node content, eg, `www.yoursite.com/special/anotherpage` is really something like `www.yoursite.com/node/123`, then you could do something like this in your theme's template.php file...

    function YOURTHEME_preprocess_page(&$vars) {
      $alias=drupal_get_path_alias($_GET['q']);
      $args=explode('/', $alias);
      if ($args[0]=='special') {
        $vars['theme_hook_suggestions'][] = 'page__special');
      }
    }

...which takes a dull ax to the url and chops it apart and if the first part is `special` then it tells drupal to use your page template for it.  If, however, you know that all of the nodes there are of a certain type, you could do it this way instead...

    function YOURTHEME_preprocess_page(&$vars) {
      if (!empty($vars['node']->type) && $vars['node']->type == 'SPECIAL_TYPE') {
        $vars['theme_hook_suggestions'][] = 'page__special');
      }
    }

...which would tell drupal to use your template file whenever it displays a SPECIAL_TYPE node on a full page.