判断弹出层登陆窗口

弹出层提示窗口  登陆验证  当错误的时候   弹出层上面提示错误 层不会消失（也就是不刷新），请问怎么写？求助各位高手，希望高手发个实例源码！谢谢啦！

ajax

ajax技术

登陆页面
<script language="javascript">
var  XHRObject=false;
if(window.XMLHttpRequest)
{
  XHRObject= new  XMLHttpRequest();
}
else{
if(window.ActiveXObject)
{
  XHRObject= new ActiveXObject("Microsoft.XMLHTTP");
}
    }
function  send()
{    
  var  f=document.getElementById('user').value;
   XHRObject.open("GET","for.php?id="+f,true);
   XHRObject.onreadystatechange= getdata;
   XHRObject.send(null);
}

function   getdata()
{  
if(XHRObject.readyState==1)
   {
  document.getElementById('checkuser').innerHTML="loading......";
   }
if(XHRObject.readyState==4 && XHRObject.status == 200)
   {
   var  text=XHRObject.responseText;
   document.getElementById('checkuser').innerHTML=text;  
   }
  
}
</script>
           <div class="left" align="center">  用 户 名：<input type="text" size="20" name="user" id="user" onBlur="send()"></div><div id="checkuser">  请输入用户名</div>
              
              <div class="left" align="center">  密      码：<input type="password" size="20" name="pass1" id="pass1" value="" onKeyPress="send2()" onBlur="return checkps1();"></div><div id="checkpass1">  请输入密码</div>

for.php页面

if($_GET[id])
{
  sleep(1);
$s="SELECT * FROM `login` where `user`= '$_GET[id]'";
  $q=mysql_query($s);
    if(is_array(mysql_fetch_row($q)))
      {  $str2=iconv("GBK","UTF-8","正确");

      echo "<font color=red>*".$str2."</font>";
      }
else
          {
          $str3=iconv("GBK","UTF-8","登陆错误");
       echo "<font color=green>".$str3."</font>";
          }
   }
}