go trough following links Tip.6..
AJAX Calender Extender[
^]
<head runat="server">
<title>Calendar Extender</title>
<script type="text/javascript">
function checkDate(sender,args)
{
var selDate= sender._selectedDate;
var today = new Date();
if (selDate.getFullYear() > today.getFullYear())
{
alert("You cannot select a day earlier than today!");
sender._selectedDate = new Date();
sender._textbox.set_Value(sender._selectedDate.format(sender._format))
}
}
</script>
</head>
<form id="form1" runat="server">
<asp:scriptmanager id="ScriptManager1" runat="server" xmlns:asp="#unknown" />
<div>
<asp:textbox id="TextBox1" runat="server" xmlns:asp="#unknown"></asp:textbox>
<cc1:calendarextender id="CalendarExtender1" xmlns:cc1="#unknown">
runat="server" OnClientDateSelectionChanged="checkDate" TargetControlID="TextBox1" />
</cc1:calendarextender></div>
</form>
..try something like this..also search for "textbox calendar extender with range validator" on google...
...same thing discussed over here
http://forums.asp.net/t/1167739.aspx/1[^][
^]