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;