Displaying widgets on seleted pages.

Hi peps,
I’m a total noob to php coding and I have no idea how i can insert this conditional tag to my code.

here’s the condition:
in_category( array( 1,2,3 ) )

here’s my code:
<?php query_posts(‘category_name=Blog &showposts=2’); ?>
<?php while (have_posts()) : the_post(); ?>
<ul class=”post_cont” id=”post-<?php the_ID(); ?>”>

• <h5>” rel=”bookmark” title=”Permanent Link to <?php the_title_attribute(); ?>”>
  <?php the_title(); ?>
  </h5>

<?php endwhile; ?>

What I want to happen is display only this code to categories 1, 2 and 3. Is this the right. Any help?

Cheers!
Eman