高手请进，看看这个登陆框是怎么做的...

<form name=auth_form method=post><input type=hidden name=userInfo value=''></form><script>
var temp=new Array();
temp[0]='http://211.100.6.72/swo/';
temp[1]='/home/groups/home/RUNMIT_PUBLIC/auth';
temp[2]='0';
temp[3]='';

var userInfo;
var undefined;
userInfo=window.showModalDialog('/RUNMIT_PUBLIC/auth/login3.php',temp,'dialogHeight:210px;dialogWidth:400px;dialogTop:50;dialogLeft:200px;status:no;scroll:no');
if(userInfo==undefined)
{
window.open('/error/authorizationRequired.html','_top','');
}
else
{
auth_form.action='/RUNMIT_PUBLIC/auth/auth.php';
auth_form.userInfo.value=userInfo;
auth_form.submit();
}
      </script>