I recall a thread with several Drupallers asking for the forum to look more like a "regular forum"
I spent a bit of time customizing my theme towards such a goal, so here's my contribution- it should work with most themes (modify as necessary)
replace your theme's comment.tpl.php with this
<div class="comment<?php if ($comment->status == COMMENT_NOT_PUBLISHED) print ' comment-unpublished'; ?>">
<h3><?php print $title; ?></h3>
<p class="submitted"><?php print $submitted; ?> <?php if ($new != '') { ?><span class="new"><?php print $new; ?></span><?php } ?></p>
<div class="usericon"><?php if ($picture) {print $picture; } ?></div>
<div class="comment-body"><?php print $content; ?></div>
<p class="links">» <?php print $links; ?></p>
</div>
then add this to the theme's style.css
.comment .submitted {margin-top: -4px; font-size: .8em;}
.comment .links {text-align: right; font-size: .9em;}
div.comment {padding: 7px 10px 0px 10px; background: #d1d1d1; border: 1px solid #444; border-right: 2px solid #222; border-bottom: 2px solid #222; margin-bottom: 20px;}
.comment-body {padding: 1px 25px 10px 80px; background: #fff; min-height: 55px;}
div.usericon {float: left; margin-right: 12px;}
tr.odd {background: #fff;}
tr.even {background: #ccc;}
td.created, {font-size: .9em; padding-top: 5px; padding-bottom: 5px;}
td.last-reply {font-size: .9em; text-align: right; padding-left: 5px;}