Loop category including custom post type

by

You would do something along these lines using the category id, and an array of the post_types within your loop

query_posts( array(
 'post_type' => array( 'post', 'report', 'opinion', bookmark' ),
 'cat' => 3,
 'orderby' => 'date',
 'order' => 'DESC',
 'showposts' => 5 )
 );

Hope that helps