how to create loading page or redirecting page on button_click?

hello friends.. 
I need some info regarding button click. I want to send mail with autorespond mail on single button click. Within that waiting time I want a screen that will show "REDIRECTING" (like gmail) and will show a "thank you" page after successfully sending the mail.
Here I am Sendin my codes....
aspx:-
<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
< ...