post_class() and <?php echo $odd_or_even; ?>

I’m using http://adambrown.info/b/widgets/easy-php-tutorial-for-wordpress-users/posts-that-have-alternating-colors/ but I don’t really know php so I don’t know how to combine it with post_class() since it generates class=””.

Currently I’m using double divs:
<div <?php post_class() ?>>
<div class=”<?php echo $odd_or_even; ?>”>

But I’d like to combine them so I only have to use one div.

Any thoughts? 🙂