How to disable current date

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="CalendarUC.ascx.cs" Inherits="CalendarUC" %>

<%@ Register Namespace="AjaxControlToolkit" Assembly="AjaxControlToolkit" tagPrefix="cc1" %>

ImageUrl="~/Images/Calendar.png" BorderStyle="Solid" BorderWidth="1px"   Height="20px" ImageAlign="Top" Width="25px" /> PopupButtonID="imgbtnCalendar" Format="dd-MMM-yyyy" runat="server" />

from my above code
i want to add code to disable current date.for that how to write the code from my above code please help m