如何在.NET 3.5 Web应用程序中安装和使用ASP.NET AJAX Control Toolkit？

 <pages>
   <controls>
      <add tagPrefix="ajaxToolkit" assembly="AjaxControlToolkit" namespace="AjaxControlToolkit"/>
    </controls>
  </pages>
</system.web>

<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajaxToolkit" %>

<ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"></ajaxToolkit:ToolkitScriptManager>

<ajaxToolkit:ModalPopupExtender ID="ModalPopupExtender1" runat="server" TargetControlID="Button1" PopupControlID="Panel1"></ajaxToolkit:ModalPopupExtender>

<asp:Button ID="Button1" runat="server" Text="Open Modal Popup" />

<asp:Panel ID="Panel1" runat="server" Style="display:none;">
  <asp:Button ID="Button2" runat="server" Text="Close" />
</asp:Panel>