linnieA on "Add class to first and last div"

Hello!

Unfortunately, my php skills aren't great, so I could really use some help on the following. I'm displaying related posts in single.php. Now I'd like to add the class .first to the first post en .last to the last post.

Here's the code I'm using:

<div id="related">
	<?php $orig_post = $post;
	global $post;
	$tags = wp_get_post_tags($post->ID);
	if ($tags) {
	$tag_ids = array();
	foreach($tags as $individual_tag) $tag_ids[] = $individual_tag->term_id;
	$args=array(
	'tag__in' => $tag_ids,
	'post__not_in' => array($post->ID),
	'posts_per_page'=>5, // Number of related posts that will be shown.
	'caller_get_posts'=>1
	);
	$my_query = new wp_query( $args );
	if( $my_query->have_posts() ) {
	echo '<div id="relatedposts"><h3>You might also like...</h3><div>';
	while( $my_query->have_posts() ) {
	$my_query->the_post(); ?>
	<div class="fourcol"><div class="relatedthumb"><a href="<? the_permalink()?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_post_thumbnail( 'related' ); ?></a></div>
	<div class="relatedcontent">
	<h2><a href="<? the_permalink()?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_title(); ?></a></h2>
	</div>
	</div>
	<? }
	echo '</div></div>';
	}
	}
	$post = $orig_post;
	wp_reset_query(); ?>
	</div>