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"; }
 }
}
document.observe("dom:loaded", function() { externalLinks(); });