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.getAttribute("rel") == "external nofollow" || 
         anchor.getAttribute("rel") == "nofollow external" )
       )

    anchor.target = "_blank";
  }
}

window.onload = function()
{
  externalLinks();
}