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.onclick = function(event){return popupWindow(this, event);}
			anchor.onkeypress = function(event){return popupWindow(this, event);}
		}
	}
}

function popupWindow(anchor, event){
	var keyCode;
	if (event && event.type == 'keypress') {
		if (event.keyCode) {
			keyCode = event.keyCode;
		} else if (event.which) {
			keyCode = event.which;
		}
		// 13 == Return key. 32 == space key
		if (keyCode != 13 && keyCode != 32)	return true;
	}
	
	return !window.open(anchor, "", "width=660,height=500");
}

Event.observe(window,'load', externalLinks, false);