sometime ago i was also interested in this topic too, basically it depends on how joomla is handling user rights. for your needs there have to be additional groups beside the basic ones like author, editor, manager, etc.
i do not know if this is already possible in joomla 1.5, in 1.x it's possible only with an extension called "jacl", but it's a kind of hack to the joomla core files.
next you would need is a newsletter component, which is able to adress the newly created groups.
cb would come into play if users should be able to send mass mails to the groups i think, as far as i remember there exists a cb 1.0 plugin bridging to a newsletter component.
hope this helps