function extLinks(){ 
	if(!document.getElementsByTagName)
		return; 
	var anchors=document.getElementsByTagName("a"); 
	for(var i=0;i<anchors.length;i++)				
		if(anchors[i].getAttribute("href")&&anchors[i].getAttribute("rel")=="external") 
			anchors[i].target="_blank";
}

window.onload=extLinks;