I'm looking for a way to publish a CMF topic object to a small group of users. What I mean by a group of user is only some members of my Plone Site. My goal is to create privates workgroups, where members of a workgroup share common components (forum, files, events, ...).

Group workspaces are coming in the next release of Plone, provided I don't get hit by a bus or something. In the meantime (it shouldn't be long, however) you can install GRUF, create a group of whomever you want, and create a folder owned by (and/or accessible only by) that group. If you want a different-than-default display or functionality, create a new Type as a copy of the Folder type and change its actions, probably to point at customized or new pages. This is basically how the group workspaces will work, and is nothing you can't do by hand. --jcc