<script language = "javascript" type="text/javascript">
    function setData(sID) {
        var targetObj = document.getElementById("idinput");
        var targetObj1 = document.getElementById(sID);
        var targetObj2 = document.getElementById('<%=iddiv.ClientID%>');
        targetObj.value = "";
        targetObj.value = targetObj1.innerHTML;
        targetObj2.innerHTML = "";
    }

    function postDataFromServer(dataSource, targetControl, datasend) {
        var myAjaxObject = false;
        var vIdInput = "idinput";
        try {
            myAjaxObject = new ActiveXObject("MSXML2.XMLHttp.5.0");
        }
        catch (exception1) {
            try {
                XMLHttpRequestObject = new ActiveXObject("MSXML2.XMLHttp.4.0");
            }
            catch (exception2) {
                try {
                    XMLHttpRequestObject = new ActiveXObject("MSXML2.XMLHttp.3.0");
                }
                catch (exception3) {
                    try {
                        XMLHttpRequestObject = new ActiveXObject("MSXML2.XMLHttp");
                    }
                    catch (exception4) {
                        if (window.XMLHttpRequest) {
                            myAjaxObject = new XMLHttpRequest();
                        }
                        else {
                            if (window.ActiveXObject) {
                                myAjaxObject = new ActiveXObject("Microsoft.XMLHTTP");
                            }
                        }
                    }
                }
            }
        }
        if (myAjaxObject) {
            myAjaxObject.open("POST", dataSource);
            myAjaxObject.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
            myAjaxObject.onreadystatechange = function () {
                if (myAjaxObject.readyState == 4 && myAjaxObject.status == 200) // при загрузке на сервер myAjaxObject.status == 404 !!!
                 {
                    var targetObj = document.getElementById('<%=iddiv.ClientID%>');
                    var t = myAjaxObject.responseText;
                    var t2 = "";
                    var s = "";
                    var f = 0;//флаг
                    var h = "";
                    for (i = 0; i < t.length; i++) {
                        if (t.substr(i, 1) == '$') {
                            f = 1;
                            h = "";
                        }
                        else {
                            if (t.substr(i, 1) == '@') {
                                f = 0;
                                t2 += "<a href='/Default.aspx?tabid=83&pid=" + h + "'>" + s + "</a></br>";
                                s = "";
                                targetObj.style.display = "";
                            }
                            else {
                                if (f == 1)
                                    h += t.substr(i, 1);
                                else
                                    s += t.substr(i, 1);
                            }
                        }
                    }
                    targetObj.innerHTML = t2;
                }
                alert(myAjaxObject.status);
            }
            myAjaxObject.send("mydata=" + datasend);
        }
    }
</script>

<table cellpadding="0" cellspacing="0" border="0" width="100%">
    <tr>
        <td align="center" style="padding:20px;">
            <div style="text-align:left;">
                <input type="text" name="idinput" style="padding:2px; height:20px; width:500px;" onkeyup ="if(this.form.idinput.value.length != 0){postDataFromServer('getajax.simple','iddiv',this.form.idinput.value)}" />&nbsp;&nbsp;<asp:Button runat="server" id="btn_search" Text="Найти" Height="30px" Width="60px"/>

                <div id="iddiv" runat="server" style="position:absolute; border:solid 1px black; background-color:Window; padding:2px; width:500px; display:none;"></div>
            </div>
            
        </td>
    </tr>
</table>

public class MyHandlerAjax : IHttpHandler
{
    bool IHttpHandler.IsReusable
    {
        get { return true; }
    }

    void IHttpHandler.ProcessRequest(HttpContext context)
    {
        HttpRequest Request = context.Request;
        HttpResponse Response = context.Response;
        string s = string.Empty;
        string s1 = string.Empty;
        string s2 = string.Empty;
        if (Request.Form["mydata"] != null)
        {
            s = Request.Form["mydata"];
        }
        if (s.Length > 3)
        {
            SqlConnection con = new SqlConnection(System.Web.Configuration.WebConfigurationManager.ConnectionStrings["SiteSqlServer"].ConnectionString);
            con.Open();
            SqlCommand com = new SqlCommand("sql запрос", con);
            SqlDataReader reader = com.ExecuteReader();
            while (reader.Read())
            {
                string sName = reader["pname"].ToString();
                string sHref = reader["id"].ToString();
                s2 += sName.Trim() + "$" + sHref + "@";

            }
            reader.Close();
            con.Close();
        }
        if (!string.IsNullOrEmpty(s2))
        {
            Response.Write(s2);
        }
    }
}

<system.webServer>
    ....
    <handlers>
      ....
      <add name="getajax" verb="*" path="getajax.simple" type="MyHandlerAjax"/>
    </handlers>
    <validation validateIntegratedModeConfiguration="false" />
  </system.webServer>
  <system.web>