function popup(url, width, height) {
	var left = (screen.availWidth/2) - (width/2);
	var top = (screen.availHeight/2) - (height/2);
	window.open(url, 'popup','scrollbars=yes, status=no, toolbar=no, location=no, directories=no, menubar=no, width=' + width + ', height=' + height + ', left=' + left + ',top=' + top);
}