Run Loop on Posts of Specific Category

Chris Coyier on
<?php query_posts('cat=5'); ?> <?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?> <?php the_content(); ?> <?php endwhile; endif; ?>

If you were to use this, for example, in a left sidebar which ran before the main loop on your page, remember to reset the query or it will upset that main loop.

<?php wp_reset_query(); ?>