Simple wp_query example

gistfile1.txt

$random_post = new WP_query(); 
$random_post->query('cat=3&showposts=1&orderby=rand'); 
while ($random_post->have_posts()) : $random_post->the_post(); 
<a href="<?php the_permalink() ?>" title="<?php the_title(); ?>">
  <img src="<?php echo get_post_meta($random_post->ID, 'featured', true); ?>">
</a>
endwhile;
wp_reset_postdata();