Four Post Images

<?php if (have_posts()) : ?>
    <?php $counter = 0; ?>
    <?php while (have_posts()) : ?>
        <?php the_post(); ?>
        <?php $counter++; ?>
        <?php $column = $counter % 4; ?>
        <?php $class = ( $column ) ? '<div class="threecol">' : '<div class="threecol last">';
    <?php if( $column == 1 ): // Open the Row?>
        <div class="row">
    <?php endif; ?>
        echo $class;
            <div id="post" <?php post_class(); ?>>
                <h2><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
                <?php if( has_post_thumbnail() ) the_post_thumbnail( 'thumbnail' ); ?>
            </div>
        </div>
    <?php if( !$column ): // Close the Row ?>
        </div>
        <div style="clear:both;"></div>
    <?php endif; ?>
    <?php endwhile; ?>
<?php if( $column ) : //Finished on an odd number close Row ?>
    <div style="clear:both;"></div>
<?php endif; ?>
<?php endif; ?>