Display custom post type

I prefer using using the array form…

$gabquery = new WP_Query(array(
    'post_type'=>'courses',//The name of the post type
    'posts_per_page'=>5, //Use this rather than showposts
    'tax_query'=>array(
         array(
          'taxonomy'=>'my-custom-tax', //Your custom taxonomy name
          'operator' => 'IN',//NOT IN & AND also available
          'field'=>'slug',//or you could select by ID
          'terms'=>array('my-term-slug')//Get posts with this term (or ID if above is ID)
         )
    )
));

The above queries posts of type ‘courses’, limits the number of posts to be displayed to 5 per page, and selects only posts which belong to the ‘my-term-slug’ term of the ‘my-custom-tax’ taxonomy.

See the WP_Query Codex.