CollapsiblePanelExtender

 <asp:Button ID="btnCustomHeaderEdit" runat="server" Text="Edit.." />
<asp:Panel ID="pnlCustomScript" runat="server">
  <table width="50%">
     <tr>
    <td style="width: 100%">
   <asp:TextBox ID="txtCustomScript" Height="100px" Width="100%" runat="server" TextMode="MultiLine"></asp:TextBox>
    </td>
   </tr>
  <tr>
   <td align="right">
  <asp:Button ID="btnCustomScriptOk" Width="45px" runat="server" Text="OK" />
    </td>
   </tr>
  </table>
  </asp:Panel>
 <cc1:CollapsiblePanelExtender ID="ajaxCE" runat="Server" TargetControlID="pnlCustomScript"

     CollapsedSize="0" Collapsed="True" ExpandControlID="btnEdit" CollapseControlID="btnCustomScriptOk"  AutoCollapse="False" AutoExpand="true" ScrollContents="false" SuppressPostBack="true"

  ExpandDirection="Vertical">

 </cc1:CollapsiblePanelExtender>