Gwolle-GB is the WordPress guestbook you've just been looking for. Beautiful and easy.
Gwolle-GB take the
the_content-hook and replaces a article/page containing [gwolle-gb] with the guestbook. You may also use
add_gwolle_gb_frontend_css(); to include the frontend CSS of Gwolle-GB and
to show the guestbook in your templates. It couldn't be easier.
If you still got problems, or if errors come up please leave a message at the WordPress forum so I can help you and fix it. Thanks!