The article you’re using is quite old, from ~2009. There are much better cleaner ways of doing commenting.
As a guide, follow this:
http://ottopress.com/2008/wordpress-2-7-comments-enhancements/
This is the definitive guide to implementing Comments post v2.7, and Otto is widely respected in the community.
Firstly, your comments code uses have_posts() to check if there are comments, instead use have_comments(), you’re also building the comment form from scratch.
Instead I recommend you use this as your base for comments.php:
http://core.trac.wordpress.org/browser/tags/3.3.1/wp-content/themes/twentyten/comments.php
It’s a good guide of how to do comments correctly with Modern WordPress. e.g. in that code the comment form is a 1 liner:
<?php comment_form(); ?>
A final word, when you include your footer, use get_footer();, and if you’re ever including a PHP template, use get_template_part() instead of the include or require directives