In a recent article, I stated that the latest adsense.module has integrated section targeting.

Today, I explain how to modify your theme so that section targeting applies to comments as well.

I am assuming that you will be using a phptemplate based theme.

What you need is  to modify the comment.tpl.php for your theme. This should look something like  this:

 <div class="comment">
 <?php if ($picture) : ?>
  <?php print $picture; ?>
 <?php endif; ?>
 <h3 class="title"><?php print $title; ?></h3>
 <?php if ($new != '') : ?>
  <span class="new"><?php print $new; ?></span>
 <?php endif; ?>
 <div class="submitted"><?php print $submitted; ?></div>
 <div class="content"><?php print $content; ?></div>
 <div class="links">&raquo; <?php print $links; ?></div>
</div>

What you need to do is wrap the content part in the section tags, like so: 

<div class="comment">
 <?php if ($picture) : ?>
  <?php print $picture; ?>
 <?php endif; ?>
 <h3 class="title"><?php print $title; ?></h3>
 <?php if ($new != '') : ?>
  <span class="new"><?php print $new; ?></span>
 <?php endif; ?>
 <div class="submitted"><?php print $submitted; ?></div>
 <!-- google_ad_section_start -->
 <div class="content"><?php print $content; ?></div>
 <!-- google_ad_section_end -->
 <div class="links">&raquo; <?php print $links; ?></div>
</div> 

That is it, this is all you need to do.