Multiple width post excepts layout

Hey i am trying to archive this layout.
https://f.cl.ly/items/0l3D0N0J1e122T3X163a/Screen%20shot%202011-08-01%20at%2017.24.35.png

The dark grey bar to the left if the sidebar and thats already done and coded,its the posts i need assistance with.

I will be using this code to display the posts in the content area.

`<?php
$the_query = new WP_Query(‘showposts=3&orderby=post_date&order=desc’);
while ($the_query->have_posts()) : $the_query->the_post(); ?>
<div class=”twentyten-latest-post”>
<?php the_post_thumbnail(array(200,9999), array (‘class’ => ‘alignleft’)); ?>
” href=”<?php the_permalink() ?>” rel=”bookmark”><?php the_title(); ?><?php the_excerpt(); ?>
<div class=”clear”></div>
</div>

<?php endwhile; ?>
<?php wp_reset_query(); ?>
‘
What i want is to be able to define a custom width for these except posts in a ‘custom field’ or in some other way,as you can see i have my 960 gs grid in place that may come in some help.I also though maybe the css3 column style?

Much appreciated ,Matt