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"))
    {
      var starget = anchor.getAttribute("rel");

      if (starget == 'external') starget = 'blank';

			anchor.target = "_" + starget;
    }
  }
}

Event.observe(window, 'load', function() { externalLinks(); });