display error msg if from date greater than to date greater

I am posting the complete aspx code to show that this is my code the main thing in this code is from date and to date which is in bold and italic i should not allow the user to enter from date greater than to date also i should not allow from date and to date not greater than todays date i need to display label messages to the user if from date is greater than to date and from date and to date should not be greater than todays date

<%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Home.aspx.cs" Inherits="Home1" %>

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