960gs different classes on teasers posts - wordpress

Question

I'm having hard time trying to use teasers post in my wordpress theme (based on 960gs), as you can see here http://img17.imageshack.us/img17/794/schermata20110420a15045.png what I got till now is one "featured" post and three teasers post with thumbnails that will probably be six (so it'll have seven posts displaied in the homepage). The problem is that to do so I have to assign a class "grid_2 alpha" to the teasers post and I don't know how to assign this class to just the first teaser on the left, lefting the other ones with no alpha or omega class and putting the omega class to just the last teaser post (the seventh).
If can help, here's the code I'm using for the loop:
<?php $firstClass = 'firstpost'; ?>
<?php /* Start loop */ ?>
<?php while (have_posts()) : the_post(); ?>
<?php if (function_exists('yoast_breadcrumb')) { if (is_page() && $post->post_parent) { yoast_breadcrumb('<p id="breadcrumbs">','</p>'); } } ?>
<div class="post <?php echo $firstClass; ?>">
<?php $firstClass = 'grid_2 alpha'; ?>
<img src="<?php echo get_post_meta($post->ID, "Thumbnail", true);?>" width="140" height="100" style="padding-bottom:20px;" />
<h1><?php the_title(); ?></h1>
<?php the_content(); ?>
<?php wp_link_pages(array('before' => '<nav id="page-nav"><p>' . __('Pages:', 'roots'), 'after' => '</p></nav>' )); ?>
</div>
<?php endwhile; // End the loop ?>
also I would like to know how I can add some text above the teaser section under the first featured post. Sorry for the too many questions and for my bad english, as you can understand I'm not a developer but I searched for one week and couldn't find anything helpful for my problems. Thanks in advance for any help, I really appreciate it.

Answer 1

<?php $count = 0; ?>
<?php /* Start loop */ ?>
<?php while (have_posts()) : the_post(); ?>
<?php $count++; ?>
<?php if ($count == 1):
$class = "firstpost';
elseif ($count == 2):
$class = "grid_2 alpha";
elseif ($count == $wp_query->post_count):
$class = "grid_2 omega";
else:
$class = "grid_2";
endif;
?>
<?php if (function_exists('yoast_breadcrumb')) { if (is_page() && $post->post_parent) { yoast_breadcrumb('<p id="breadcrumbs">','</p>'); } } ?>
<div class="post <?php echo $class; ?>">
<img src="<?php echo get_post_meta($post->ID, "Thumbnail", true);?>" style="padding-bottom:20px;" />
<h1><?php the_title(); ?></h1>
<?php the_content(); ?>
<?php wp_link_pages(array('before' => '<nav id="page-nav"><p>' . __('Pages:', 'roots'), 'after' => '</p></nav>' )); ?>
</div>
<?php endwhile; // End the loop ?>