$(document).ready(function() {
  $('dl.left_nav > dd').hide();
  $('dl.left_nav > dt').click(function() {
    var $nextDT = $(this).next();
    var $visibleSiblings = $nextDT.siblings('dd:visible');
    if ($nextDT.text() == '') {
      $visibleSiblings.slideUp();
    } else {
      if ($visibleSiblings.length) {
        $visibleSiblings.slideUp('slow', function() {
          $nextDT.slideToggle('slow');
        });
      } else {
         $nextDT.slideToggle('slow');
      }
    }
  });

});