Attachment galore

Hi all,

I’m trying to create a list of images, using my own “sizes”. Something like
wp_get_attachment_link ( $attachment->ID, 'header' );
comes close, but it returns the header-image and link to the large (original) image. I don’t need the link, I want the URI – and that of it’s smaller brother (‘navthumb’).

The following is als very close, but only returns the results of ONE attachment and not all.

<?php if ( have_posts() ) : while ( have_posts() ) : the_post();

        $args = array(
          'post_type' => 'attachment',
          'numberposts' => -1,
          'post_status' => null,
          'post_parent' => $post->ID
          );

        $attachments = get_posts( $args );
          if ( $attachments ) {
            foreach ( $attachments as $attachment ) {

     $header_image_url = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID),'header');
     $thumb_image_url = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID),'navthumb');
 echo $header_image_url[0];
 echo $thumb_image_url[0];

        endwhile; endif; ?>

Anyone?