Define your cat id hear ‘category__in’ => array(2, 6),
<?php
$orig_post = $post;
global $post;
$args = array(
'category__in' => array(2, 6),
'post__not_in' => array($post->ID),
'posts_per_page' => 2,
'caller_get_posts' => 1
);
$my_query = new wp_query($args);
if ($my_query->have_posts()) {
echo '<div id="related_posts"><h3>Related Posts</h3><ul>';
while ($my_query->have_posts()) {
$my_query->the_post();
?>
<li><div class="relatedthumb"><a href="<? the_permalink() ?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_post_thumbnail(); ?></a></div>
<div class="relatedcontent">
<h3><a href="<? the_permalink() ?>" rel="bookmark" title="<?php the_title(); ?>"><?php the_title(); ?></a></h3>
<?php the_time('M j, Y') ?>
</div>
</li>
<?
}
echo '</ul></div>';
}
$post = $orig_post;
wp_reset_query();
?>