function theme_primary_menu_links($primary_links) {
  global $user;

  $output = '';
  if (module_exists('nice_menus') && arg(0) != 'admin') {
    $pid = variable_get('menu_primary_menu', 0);
    if ($menu_tree = theme('nice_menu_tree', $pid)) {
      if ($menu_tree['content']) {
        // Hacking in a conditional signup tab here...
        $register = $user->uid ? '' : '<li>'. l(t('Login/Register'), 'user') .'</li>';
        $output .= '<ul class="nice-menu nice-menu-down" id="nice-menu-primary">'. $register . $menu_tree['content'] .'</ul>';
      }
    }
  }
  else {
    $output .= theme('menu_links', $primary_links);
  }
  return $output;
}