I'm trying this:
<?php query_posts('cat=6'); ?>
<?php if (have_posts()) : ?>
<?php while (have_posts()) : the_post(); ?>
<div>
<?php $counter=3; ?>
<?php the_post_thumbnail(); ?>
<?php $counter++; ?>
</div>
<?php endwhile; ?>
<?php endif; ?>
But it's not working! :/ Thank you!
I haven't tested it with wordpress so i'm not 100% sure it'll work. The idea is to use the modulus operator (see an example that matches your needs here http://codepad.org/78d2aAKp)
Thanks for your support guys! :) I tried both solutions but didn't work, I ended up with this and works perfectly!