function ajax(file, id, params, next_function){
  var send, ajax_object = false;
  if(window.XMLHttpRequest){
    ajax_object = new XMLHttpRequest();
  }
  else if(window.ActiveXObject){
    ajax_object = new ActiveXObject("Microsoft.XMLHTTP");
  }
  if(ajax_object){
    if(params){
      send = "";
      for(i in params){
        i = encodeURI(i).replace(/\&/g, "%26");
        params[i] = encodeURI(params[i]).replace(/\&/g, "%26");
        send += i+"="+params[i]+"&";
      }
      send = send.substr(0, send.length-1);
      ajax_object.open("POST", file, true);
      ajax_object.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
      ajax_object.setRequestHeader("Content-length", send.length);
      ajax_object.setRequestHeader("Connection", "close");
    }
    else{
      send = null;
      ajax_object.open("GET", file, true);
    }
    ajax_object.onreadystatechange = function(){
      if(ajax_object.readyState==4 && ajax_object.status==200 && id!=""){
        document.getElementById(id).innerHTML = ajax_object.responseText;
        if(next_function=='show_new') show_new();
      }
    }
    ajax_object.send(send);
  }
}