function externalLinks() {
 if (!document.getElementsByTagName) return;
 var anchors = document.getElementsByTagName("area");
 for (var i=0; i<anchors.length; i++) {
   var anchor = anchors[i];
   if (anchor.getAttribute("href") &&
       anchor.getAttribute("class") == "extarea")
     anchor.target = "_blank";
 }
}
window.onload = externalLinks;

/* call using at the top of each site page
<script type="text/javascript" src="css/external.js">
</script>
*/