请问大家,asp中怎么样写才能自动检测用户名，急！谢了

<script language="javascript">
function getMyHTML(serverPage, objID, IFID) {
var obj = document.getElementById(objID);
var IF = document.getElementById(IFID);

IF.src=serverPage;

}
//=======================
function CheckUserName()
{
getMyHTML("memberregcheck.asp?operator=usernamenotic&userName="+document.regform.username.value, "usernamenotic","check");
}
}
</script>

<form name="regform" method="post" action="memberregpost.asp" onSubmit="return checkform()"><tr>
<td width="133" bgcolor="#F6F6F6"><div align="right"><span style="color: #FF0000">*</span> 会员帐号:</div></td>
<td colspan="2" bgcolor="#F6F6F6">