post-thumbnails / add_image_size ?

Hi all

I’m using this code to add post-thumbnails and add support for different sizes

<?php
  if( function_exists( 'add_theme_support' )){
    add_theme_support('post-thumbnails');
    set_post_thumbnail_size(150,150);
  }
  if( function_exists( 'add_image_size' )){
    add_image_size('portfolio-item',442, 362, true);
    add_image_size('portfolio-example',300, 300, true);
    add_image_size('featured',602, 282, true);
    add_image_size('service',140, 140, true);
  }
?>

Should the sizes for ‘portfolio-item’, ‘portfolio-example’ etc. show up on the Featured Image window . At the moment they don’t show there, am I doing something wrong?