Checking Username

Hi
I'm need to check the user name available or not using ajax/javascript.
I have the code as below
<asp:TextBox ID="profileid" runat="server"></asp:TextBox>
<script type="text/javascript">
function validateuser()
{
var oField = document.frm_registration.profileid.value;
alert(oField);
        sUrl = "http://192.168.1.45/r e/check.aspx?login="+oField;
        alert(sUrl);
}
</script>
in cs page 
profileid.Attributes.Add("onblur", "return validateuser();");
 
in check.aspx page load I have given the code as below
        string user = Request.QueryString.Get("login");
        string strResult = null;
&n ...