filter asides from recent entries list

Hey guys I’m using this hack to display a list of recent entries on my wordpress blog.

foreach ($posts as $post) {
$post_title = stripslashes($post->post_title);
$permalink = get_permalink($post->ID);
$output .= $before . '<a href="' . $permalink . '" rel="bookmark" title="Permanent Link: ' . $post_title . '">' . $post_title . '</a>' . $after;
}
echo $output;


My problem is im still a little new to wordpress and I was wondering how I would go about figuring out what categories belong to a certain post so that I can filter out the asides category from being shown on the list?

Any help would be great. Thank you