Is there any way that I can add a short message to the custom posts type page in - ie the page where the posts are listed. I have checked the codex and searched the web to no avail.
Good question. I've often wondered it myself. This will work. You just need to change my_post_type_slug to the slug of your post type. There might be a cleaner way to find the post type other than using $_GET but it's good enough for now!
I'm not a full fledged wordpress guru like others here on the forum, so the way I solve these issues is look in the source of the admin, find something unique, then do a site-wide search for that text. then in whatever file I end up in, I search around for an add_action hook.
AND there is another way to do it too. But It's a hack. You can use the view_ filter which is meant to piece together an array of view options at the top of the screen. You can always output html in the hook and return the passed variable. It's a hack because they could move the position of this hook in the future and your code might not output in the right place anymore. but it's handy considering the total lack of actions in the custom post type admin head. The nice thing about this is that it outputs right after the title.