var tables = document.getElementsByTagName('table');
for(var i = 0; i < tables.length; ++i){
  if(tables[i].parentNode.id == 'ad_fix'){
    var trs = tables[i].getElementsByTagName('tr');
    if(trs.length > 0){
      var tds = trs[trs.length - 1].getElementsByTagName('td')[0];
      tds.innerHTML = '<center><a style=\"font-size:10px;color:#0000ff;line-height:1.2;text-decoration:none;font-weight:bold;background-color:#ffffff;font-family:Tahoma, verdana,arial,helvetica,sans-serif;text-transform: none;letter-spacing:normal;text-shadow:none;white-space:normal;word-spacing:normal;\" href=\"http://www.projectwonderful.com/advertisehere.php?id=47430&type=7\" target=\"_blank\">Ads by Project Wonderful!</a></center>';
    }
  }
}