// 封装下 Propertyt 的 AJAX 召唤方法
function callAjax(url, method, postBody, callBack)
{
	new Ajax.Request(url, {
	  encoding: "UTF-8", 
	  method: method,
	  postBody: postBody,
	  onSuccess: function(transport) {
		callBack(transport.responseXML);
	  }
	});
}