Torben,
I just build what you are suggesting (I think)
this set up over the weekend, using the default categorisation function of bboard in Openacs 3.2.5 It will do just this. Maybe I don't see the problem you are describing. Any way, for the time beeing, newbies would be very happy to have an environment like this on the curent openacs site. What I described above can be set up in about 1 hour. It's not rocket science, but it works fine.
Cheers