Posts per row

How to do that it would be 4 posts per row ?
if i change $counter==2 to $counter==4 it bugs. Any ideas ?

<?php $counter=1;global $query_string;query_posts($query_string.'&caller_get_posts=1&posts_per_page=9');if(have_posts()):while(have_posts()):the_post();if($counter==1):?>

<div class="post_row">
<div class="post_class"><?php elseif($counter==2): ?><div class="post_class"><?php endif; ?>

<a href="<?php the_permalink();?>"><?php the_post_thumbnail('default-thumb')?></a>
<h2><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
<?php the_excerpt() ?>
</div><!-- /.col -->

<?php if($counter==2): ?></div><!-- /.row cols2 -->
<?php $counter=0;endif;$counter++;endwhile;if($counter==2):?></div><!-- /.row cols2 --><?php endif;endif; ?>