Multiple Categories on 1 Page

Hi there I’m very new to WordPress and PHP/CSS so I have used a theme and modified it to look how I wish, but what I want to do now is on one page (ID 179) I want to pull in the posts from 2 categories (ID 12 and 87). The reason for this is I want the page to have different information that is static at the top and then pull in the post excerpts.

As I said I’m new to PHP but this is what I have so far:

<div class="entry">
<?php if (is_page(179)) : ?>
<?php THIS IS WHERE IM STUCK ?>
     <?php else : ?>
<?php the_content(); ?>
     <?php endif; ?>
<?php link_pages('<p><strong>Pages:</strong>','</p>','number'); ?>
</div>

I have searched the forum and Docs but can’t quite find what I do to pull in excerpts of posts for categories ID 12 and ID 87?

I would really appreciate any help

Mark