var http_request = false;
  function create_request(){
	http_request = false;
	  if(window.XMLHttpRequest){
		http_request = new XMLHttpRequest();
		if(http_request.overrideMimeType){
			http_request.overrideMimeType('text/xml');
		}
	  }else if(window.ActiveXObject){
		  try{
			  http_request = new ActiveXObject('Msxml2.XMLHTTP');
		  }catch(e){
			try{
			   http_request = new ActiveXObject('Microsoft.XMLHTTP');
			}catch(e){
				http_request = false;
			}
		  }
	  }
	  if(!http_request){
		  window.alert('创建 XMLHttpRequest 对象失败.');
		  return false;
	  }
  }
  function send_request(url,func){
	  create_request();
	  http_request.onreadystatechange = func;	  
	  http_request.open("GET",url,true);
	  http_request.setRequestHeader("If-Modified-Since","0");
	  http_request.setRequestHeader("Cache-Control","no-cache");
	  http_request.send(null);
  }
  function process_request(id){	  
	  if(http_request.readyState != 4){		
	      document.getElementById(id).innerHTML = "<img src=\"images/loading.gif\" align=\"middle\" alt=\"正在加载\"/>";		 
	  }else if(http_request.readyState == 4){ 		  
		  if(http_request.status == 200){			  
			  document.getElementById(id).innerHTML = http_request.responseText;
		  }else{
			  alert('加载文件失败，请刷新！');
			  return false;
		  }
	  }
  }