hello dude try this code may be help full..
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
<title></title>
<style type="text/css">
.modalBackground
{
background-color:#CCCCFF;
filter:alpha(opacity=40);
opacity:0.5;
}
.ModalWindow
{
border: solid1px#c0c0c0;
background:#f0f0f0;
padding: 0px10px10px10px;
position:absolute;
top:-1000px;
}
</style>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<cc1:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="lnkPopup" PopupControlID="panEdit" BackgroundCssClass="modalBackground" CancelControlID="btnCancel" PopupDragHandleControlID="panEdit"></cc1:ModalPopupExtender>
<a id="lnkPopup" runat="server">Show Popup</a>
<asp:Panel ID="panEdit" runat="server" Height="180px" Width="400px" CssClass="ModalWindow">
<h1>Edit</h1>
<table width="100%">
<tr>
<td class="formtext" style="height: 23px; width: 150px;" align="left">
Fields1:
</td>
<td>
<asp:TextBox ID="txtFields1" runat="server"></asp:TextBox>
<cc1:CalendarExtender runat="server" ID="ss" TargetControlID="txtFields1" ></cc1:CalendarExtender>
</td>
</tr>
</table>
<br />
<asp:Button ID="Button1" runat="server" Text="Update" />
<asp:Button ID="btnCancel" runat="server" Text="Cancel" />
</asp:Panel>
</div>
</form>
</body>
</html>