Shortcode for Custom Post Type

Hi I am having trouble with a shortcode that pulls information from a Custom Post Type. A manage to pull the data, but all of it, however I am only wanting to extract a category of the custom post type.

/* Insiders */

register_taxonomy('insidersguidecat', 'insidersguide', array('hierarchical' => true, 'label' => __('Insiders Guide Categories'), 'singular_name' => 'Category'));
}
add_action('init', 'gr_post_type_insidersguide');

/* Shortcode */ This shortcode draws the information.

function gr_town($atts, $content = null) {
extract(shortcode_atts(array(
                "numposts" => '5',
	), $atts));
	query_posts('post_type=insidersguide&showposts='.$numposts);

The code that doesn’t filter the information I want

function gr_town($atts, $content = null) {
extract(shortcode_atts(array(
                "numposts" => '5',
		"taxonomy_name" => "term_name"

	), $atts));
	query_posts('post_type=insidersguide&'.term_name.'&showposts='.$numposts);

Any ideas?