Exclude category from loop grid

Currently I am showing all recent posts on my homepage in a 2 column grid layout. It works just fine with this code:

<div id="gridcontainer"> 

<?php
$counter = 1; //start counter
$grids = 2; //Grids per row
global $query_string; //Need this to make pagination work
/*Setting up our custom query (In here we are setting it to show 12 posts per page and eliminate all sticky posts) */
query_posts($query_string . '&caller_get_posts=1&posts_per_page=12');

if(have_posts()) :	while(have_posts()) :  the_post();
?>
<?php
//Show the left hand side column
if($counter == 1) :
?>
			<div class="griditemleft">
                 <h2 class="entry-title"><a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>
			    <div class="format_teaser entry-content"><p><?php the_excerpt(); ?></p></div>
            </div>
<?php
//Show the right hand side column
elseif($counter == $grids) :
?>
<div class="griditemright">
                <h2 class="entry-title"><a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>
			    <div class="format_teaser entry-content"><p><?php the_excerpt(); ?></p></div>
            </div>
<div class="clear"></div>
<?php
$counter = 0;
endif;
?>
<?php
$counter++;
endwhile;
//Pagination can go here if you want it.
endif;
?>
</div>

What I need to do is exclude category ID = 1.

Suggestions, please?