function externalLinks() {
 if (document.getElementsByTagName)
 {
 var anchors = document.getElementsByTagName("a");
 for (var i=0; i<anchors.length; i++) {
   var anchor = anchors[i];
   if (anchor.href &&
       anchor.className == "extern")
     anchor.target = "_blank";
 }
 }
}
window.onload = externalLinks;