It's because you've not placed the php-code inside <?php and ?>. The correct code is
...
?>
<script type="text/javascript" src="http://www.footerchat.com/chat/cons.js"></script>
<?php
if (!$forum_user['is_guest'])
echo '<script type="text/javascript">autoLogin("'.$forum_user['username'].'");</script>';
?>
<p id="copyright"><?php echo sprintf($lang_common['Powered by'], '<a href="http://punbb.informer.com/">PunBB</a>'.($forum_config['o_show_version'] == '1' ? ' '.$forum_config['o_cur_version'] : ''), '<a href="http://www.informer.com/">Informer Technologies, Inc</a>') ?></p>
<?php
...