<?php if (have_posts()) : ?>
<?php while (have_posts()) : the_post(); $loopcounter++; ?>
// the loop stuffs
<?php if ($loopcounter <= 1) { include (TEMPLATEPATH . '/ad.php'); } ?>
<?php endwhile; ?>
<?php else : ?>
<?php endif; ?>
Quelle: http://www.webdesignerwall.com/tutorials/wordpress-theme-hacks/
