Display most recent posts in category with Twenty Ten theme widget

Question

I am fairly new to WordPress, and I would like to have a list of the most recent posts in a certain category appear in a right-hand panel (I can do this with all posts, but not specific categories)

I am using the Twenty Ten theme, on wordpress.com. I have found the following code, but unsure if or where this can be added:

<ul>
<?php $recent = new WP_Query("cat=10&showposts=5"); while($recent->have_posts()) : $recent->the_post();?>
    <li><a href="<?php the_permalink() ?>" rel="bookmark"><?php the_title(); ?></a></li>
    <?php endwhile; ?>
</ul>

Answer 1

The fastest way, a plugin:

http://wordpress.org/extend/plugins/category-posts/

Answer 2

You are using wordpress.com. You cannot modify your Theme template files, or upload Plugins. You are limited to the Plugins available via Dashboard -> Plugins.