get content from category 5 with wpdb

i have this code:

$rand_id = $wpdb->get_var("SELECT ID FROM $wpdb->posts WHERE post_status = 'publish' ORDER BY RAND() LIMIT 1");
      query_posts("p=$rand_id");
	while (have_posts()) : the_post();
	the_title();

endwhile;

The code retrive random article titles from the entire blog.
What i want is to retrive content from only one category, for ex category ID 5.

Thank you.