Custom posts type with custom taxonomy

I having some difficulty figuring out how to query a custom post type in a specific (custom) taxonomy.

So far I have the following code:

<?php query_posts( array('post_type' => array('post','tvshows'), 'showposts' => $nitem, 'orderby' => 'date' )); ?>
<?php while ( have_posts() ) : the_post(); ?>
<?php   if (has_post_thumbnail()) {
$imgsrc = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID),'medium');
$imgsrc = $imgsrc[0];
} elseif ($postimages = get_children("post_parent=$post->ID&post_type=attachment&post_mime_type=image&numberposts=0")) {
foreach($postimages as $postimage) {
$imgsrc = wp_get_attachment_image_src($postimage->ID, 'medium');
$imgsrc = $imgsrc[0];
}
} elseif (preg_match('/<img [^>]*src=["|\']([^"|\']+)/i', get_the_content(), $match) != FALSE) {
$imgsrc = $match[1];
} else {
$img = get_post_custom_values('poster_url');
$imgsrc = $img[0];
} ?>

I have tax for “cast”. For example use the name: alexandro. How to filter post by my taxonomy? I’ve tried, but fail. ??