Modifying CCK fieldgroups with hook_form_alter()

I was writing a module to conditionally hide a fieldset on a CCK node editing form based on whether the user is logged in or not, and for a while I was very puzzled as to why my custom module's implementation of hook_form_alter wasn't seeing any of the fieldsets defined by the CCK fieldgroup module.

I searched Google for the terms 'cck fieldset hook_form_alter', which led me to a helpful tip from Benjamin Melançon: