How to query and display one post in the sidebar

I don’t know how correct this is, I am not a php programmer. However, this is what I have done in the sidebar, you’ll just have to modify it from category name / show 1 post, to using post id (you can find that info in the codex).

<?php query_posts('category_name=news&showposts=1'); ?>
  <?php while (have_posts()) : the_post(); ?>
   <h2 class="entry-title"><a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title() ?></a></h2>
 <?php the_post_thumbnail(array(100,100), array('class' => 'alignleft post_thumbnail'));?>
              <?php the_content() ?>
       <div class="clear"></div>
  <?php endwhile;?>

Hi wpit,
You can try :

<?php
//First we select the post id that you want to use ex: 5
query_posts( 'p=5' );
//then the loop stats here:
if ( have_posts() ) : while ( have_posts() ) : the_post();
//and ends here :
endwhile; else: ?>
<p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
<?php endif; ?>

Regards

Thank you guys,
Both worked, jnhghy was more specific to what I was looking for. After testing I also found out that you need <?php wp_reset_query(); ?> at the of the<?php endif; ?> if not single.php will always display the one post I am querying.

Thanks,