<?php

$cats = array('1','2','3'); //enter your 3 category IDs

$num_blocks=7;

$results =array();

foreach ($cats as $cat){

	query_posts('cat='.$cat.'&posts_per_page='.$num_blocks);



	$i=0;

	while (have_posts()): the_post();

		if($i<=$num_blocks){

			$results[$i][] = get_the_ID();

		}

		$i++;

	endwhile;

	wp_reset_query();

}



foreach ($results as $result){



	query_posts(array('post__in'=>$result));

	while (have_posts()): the_post();

	?>

	<div class="cats">

	<li>



		<h2><a href="<?php the_permalink() ?>"><?php the_title(); ?></a></h2>



		<!-- <div class="post" id="post-<?php the_ID(); ?>"><?php the_excerpt(); ?></div> -->



	</li>

	</div>



	<?php

	endwhile;

	echo '<hr />';

	wp_reset_query();

}

?>