gistfile1

in functions.php

if ( function_exists( 'add_theme_support' ) ) {
    add_theme_support( 'post-thumbnails' );
    set_post_thumbnail_size( 150, 150 ); // default Post Thumbnail dimensions
    add_image_size('homepage-image', 327, 218, true);
    add_image_size('single-image', 675, 450, true);
}

then in the single.php i have

<?php
$images =& get_children('post_type=attachment&post_mime_type=image&post_parent=' . $post->ID );
foreach ($images as $image) : ?>
    <li><?php echo wp_get_attachment_image($image->ID, 'single-image'); ?></li>
<?php endforeach ?>