<script type="text/javascript">
function checkDate(sender,args)
{
if (sender._selectedDate < new Date())
{
alert("You cannot select a day earlier than today!");
sender._selectedDate = new Date();
// set the date back to the current date
sender._textbox.set_Value(sender._selectedDate.format(sender._format))
}
}
</script>
and on extender textbox you have to call checkdate function
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<cc1:CalendarExtender ID="CalendarExtender1"
runat="server" OnClientDateSelectionChanged="checkDate" TargetControlID="TextBox1" /
this can give you better idea how to customize you control according to any requirment.
if you have any other question regarding to development .please feel free to contact
http://www.visiostudio.net or mail me at
info@visiostudio.net