I try and I try but with no resuts; OK, what I do:
1) I modify first the alias value from "webmail" to "sqm" in squirrelmail.conf
2) I edit httpd.comf and I add Alias /sqm/   /usr/share/squirrelmail
3) I add <Directory> values
OK, averything fine, I test the config, response OK, restart services (apache and intd) and when I go to 
http://192.168.1.1/sqm the response is the txt file of index.php
---------------
<?php
/**
 * index.php
 *
 * Redirects to the login page.
 *
 * @copyright © 1999-2006 The SquirrelMail Project Team
 * @license 
http://opensource.org/licenses/gpl-license.php GNU Public License
 * @version $Id: index.php,v 1.14.2.7 2006/02/03 22:27:46 jervfors Exp $
 * @package squirrelmail
 */
// Are we configured yet?
if( ! file_exists ( 'config/config.php' ) ) {
    echo '<html><body><p><strong>ERROR:</strong> Config file ' .
        '"<tt>config/config.php</tt>" not found. You need to ' .
        'configure SquirrelMail before you can use it.</p></body></html>';
    exit;
}
// If we are, go ahead to the login page.
header('Location: src/login.php');
?>
-----------------------------
Strange? What's mean this? PHP is not active? Need some help...