All comment stuff is done through “calling”: comments_template.php

THEN: editing comments.php … that is, through there, you can edit and so on, the formatting of the comments etc.
Interesting Plugins that should be used:

Using Gravators with your comments:
http://zenpax.com/gravatars2/
(FYI: Gravators.com –> and their native plugin for Wordpress … check it out!)
Author Highlite –>
http://dev.wp-plugins.org/wiki/AuthorHighlight
Recent Comments –>
http://blog.jodies.de/archiv/2004/11/13/recent-comments/