Make sure you have duplicated your templates, then look for the menu coding in the "system" catergory.
Find the mainmenu code, copy & paste it into the username one.
Save it.
Why you want to do this way? having the same appearance?
function redirect_header($url, $time = 3, $message = '', $addredirect = true)
function redirect_header($url, $time = 0, $message = '', $addredirect = false)
<?php
include("mainfile.php");
?>