Simple Code Help needed

I’m trying to display all entries posted on the current day from one particular category only.

Here’s what I’ve found. What do I need to add so that it only shows posts from the cat=id that i specify ? Thanks.

<ul>
<?php $today = getdate(); query_posts ('year=' .$today["year"] .'&monthnum=' .$today["mon"] .'&day=' .$today["mday"] ); ?>

  <?php while (have_posts()) : the_post(); ?>
<li>
    <!-- STUFF HERE -->
</li>

  <?php endwhile;?>
</ul>