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") == "external"))
    {
      anchor.target = "_blank";
    }
  }
}

addLoadEvent(externalLinks);