function externalLinks()
{
  if (!document.getElementsByTagName) return;
  var anchors = document.getElementsByTagName("a");
  for (var i=0; i<anchors.length; i++)
  {
    var anchor = anchors[i];
    if (anchor.getAttribute("href") &&
        anchor.getAttribute("rel") &&
        anchor.getAttribute("rel").indexOf("external") > -1)
      anchor.target = "_blank";
  }
}
addEvent(window,'load',externalLinks);