Someone

  <?php if (isset($primary_links)) { ?>
    <div id="primary"> <?php
  $primary_links_id = 2;
  $primary_links = '';
  $m = menu_get_menu();
  $m = $m['visible'];
  var_dump($m[$primary_links_id]);
  foreach ($m[$primary_links_id]['children'] as $mid) {
    $menu = menu_get_item($mid);
    $title = $menu['title'];
    $path = $menu['path'];
    $cls = strtolower(str_replace(' ', '_', $title));
    $primary_links .= "<a class='$cls' href='$path'>$title</a>";
  }
  print($primary_links);
?></div>