Asp calendar control

Question

 ID="Calendar1" runat="server" ShowTitle="true" ShowNextPrevMonth="true" DayNameFormat="FirstTwoLetters" />
 ID="Calendar2" runat="server" ShowTitle="true" ShowNextPrevMonth="true" DayNameFormat="FirstTwoLetters" />

 

 

I have two calendars in my web page .One is to Select for a from date and another one is for selection of to date .If i select a date from calendar 1 then i wish to hide the dates   before the selected date of cal 1 in calendar 2.can anyone suggest how to do?.