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