Hi to follow this thread : http://www.zenphoto.org/support/topic.php?id=9258
and made a little plugin that print a Back To Top link on the news.php and pages.php files for your Blog section.

Thank to Acrylian for the help.

Download and information and see it in action here http://www.latitudes-photos.com/zenphoto

Laurent

Thanks, will add it to the extensions section later.