function external() { 
 if (document.getElementsByTagName) {
  var i;
  var anchors = document.getElementsByTagName('a');
  for (var i=0; i < anchors.length; i++) {
  	var anchor = anchors[i];
   	if ((anchor.getAttribute) && (anchor.getAttribute('href') && 
       anchor.getAttribute('class') == 'external')) {  anchor.target = '_blank'; }
  }
 }
}

window.onload = external;