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";  
  }  
}  
window.onload = externalLinks;