At the moment there exists the ability to select usernames in guppy with a plugin (and I believe this feature is being integrated into the next release of pagesetter- big thanks for that guys!)
It would be rather swell if that while this feature was being hardcoded into pagesetter the ability to select PostNuke Gropus was also added.
Currently this can be achieved (kind of) by coding permissions in the template and manually typing in the group or creating a list of groups but it's necessary to have a plugin to do it automatically...