function resolveExternalLinks() {	
	if (!document.getElementsByTagName || !$) return;
	
	var arrA = $A(document.getElementsByTagName("a"));

	arrA.each(function(objChild){
		if(objChild.getAttribute("href") && objChild.getAttribute("rel") == "external"){
			objChild.target="_blank";
		}
	});
}
Event.observe(window, 'load', resolveExternalLinks);