function HandleExternalLinks() {
  if (document.getElementsByTagName) {
    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";
      }
    }
  }
}

window.onload = HandleExternalLinks;