Hey Ladygeekgeek,
I’m a newbie myself. Most of what I’ve managed to here has been from the WordPress Codex (long live OpenSource!).
I do know, however, that attachments don’t have excerpts, just captions and descriptions. I think you can get what you need by replacing the function with this:
function im_mediatags($post_item, $size='')
{
$image_src = wp_get_attachment_url($post_item->ID, $size);
return '<li class="media-tag-list" id="media-tag-item-'.$post_item->ID.'"><a
href="'.$image_src.'" target="_blank">'.$post_item->post_title.'</a> <br/>'.$post_item->post_content.'</li>';
}
Basically, just replace post_excerpt with post_content. You need a full stop before and after the php element, and you will have css and display issues if you put in a second list (li) item, so keep all elements between single li tags. A second li item will make it look like a separate attachment, as each list item will be styled exactly the same as the last. Better to span tags before and after the description in order to style it.