function popup(URL,windowName,width,height) {
	if (!width) {
		width = 500;
	}
	if (!height) {
		height = 500;
	}
	return windowName = window.open(URL,'',	'scrollbars=no,toolbar=no,location=no,status=no,menubar=no,resizable=no,left='+((screen.width-width) / 2)+',top='+((screen.height-height) / 2)+',width=' + width + ',height=' + height);
}