Need direction on customizing code

I think what I need to do is insert this snippet between my existing code to call from one category?

So:

<?php while (have_posts()): the_post(); ?>
<?php endwhile; ?>

would become

<?php while (have_posts()): the_post(); ?>
<?query_posts('cat=-3'); ?>
<?php endwhile; ?>

With the number 3 being replaced with my category name. Is this right?

Thanks everyone, read the articles and used your code examples to accomplish what I needed!

Here’s what my final code looks like:

<div id="rightcol2">
    <p><img src="../images/tipsheader.gif" width="204" height="37"></p>
    <div class="item">
      <?php if (have_posts()) : ?>
      <?php $temp_query = $wp_query; ?>
      <?php query_posts('category_name=tips&amp;showposts=1'); ?>
      <?php while (have_posts()) : the_post(); ?>
      <small>
      <?php the_time('F jS, Y') ?>
      <!-- by <?php the_author() ?> -->
      </small>
      <div class="entry">
        <?php the_content('Read the rest of this entry &raquo;'); ?>
      </div>
    </div>
    <?php endwhile; ?>
    <?php else : ?>
    <?php endif; ?>
  </div>

It shows one post from the category “tips”. Awesome!!!

Just in case anyone cares, my head code reads like this:

<?php define('WP_USE_THEMES', false); get_header(); ?>
require('../wordpress/wp-blog-header.php');
query_posts('showposts=1');
?>

Thanks everyone!