Drupal 7: You can find a Drupal 7 version of the module here!
This module allows you to create field groups for CCK fields. So you can
group your CCK node forms with the help of field groups.
Field groups can be set to be collapsible and can have descriptions.
This module has been incorporated into the Content Construction Kit (CCK). Use the latest release of it and fieldgroup will be included!
If you had fieldgroup installed manually before, don't forget to remove the old module, so that the module provided with CCK will be used!
Also submit any issues into the cck issue queue!