Loop a category from a custom post type

I’m using custom post types and want to loop posts from a particular category in a custom post type. (I’m using this category as a checkbox for whether or not it should appear on the homepage).

Currently, I am using the following code which is showing all of the posts from the custom post type, rather than just the category. I’ve tried filtering the category by number but it doesn’t want to play ball.

Any ideas?

This is the code that is doing the filtering at the moment:

<?php query_posts('post_type=book','category_name=new_release'); ?>