Today PlaatSoft released Addressbook 5.x-3.4 for Drupal 5
15-09-2009 Version 5.x-3.4
- Use file_directory_path() function instead of hardcoded /files definition.
- Improve address.info information.
- Updated drupal.org addressbook cvs repository for automatic update detection.
- Final version for Drupal 5.x


It would help to have a demo of the addressbook module on your plaatsoft.nl website and link it from the drupal page (http://drupal.org/project/addressbook), so web developers can have a sense of the features of the module prior to installation.
Thanks for the tip. I have added two demo (Drupal 5 and Drupal 6) sites on the (http://drupal.org/project/addressbook) page!