function popup(url, title, width, height) {

	var left = Math.ceil((window.screen.availWidth - width) / 2);
	var top = Math.ceil((window.screen.availHeight - height) / 2);

	window.open(url, title, "menubar=no,status=no,scrollbars=no,resizable=yes,width=" + width + ",height=" + height + ",top=" + top + ",left=" + left);
}