How to have Adsense appear under the first post in Wordpress blog?

To have Adsense codes only appear after the first post in Wordpress blog and nowhere else, open the index.php file and search for the following lines:

<!--p if (have_posts()) -->
<!--p $postCount=0;-->
<!--p while (have_posts()) : the_post(); $loopcounter++-->
<!--p $postCount++-->

Add the following above these lines:

<?php
$postnum = 1;
%2tshowadsense1 = 1;
?>

After that search for the following lines in the same index.php file:

<?php if ($loopcounter == 1) { include (TEMPLATEPATH . '/ad_middle.php'); } ?>
</div>
*** Take note about this gap ***
<?php endwhile; ?>

Add the following scripts into the gap:

<?php if ($postnum == $showadsense1) {
echo '

*** Put your Adsense Script here ***
';

} ?>

<?php $postnum++; ?>

By the way, the version of Wordpress tested was Wordpress 2.6.3. Not sure if other version of Wordpress are havi.g the same coding in index.php or not ... Anyway, worth a try.