Hello Rafael,
Good question :) The fact is that if you are fluent with RDBMS concepts, TCL and Nerdish enough, you can learn OpenACS... But if you have to learn the concepts of RDBMS from scratch, I would think it's much more difficult. Why Zope? We have some Zope installations and that person should be able to "understand" a little bit of it so he/she could give some support to the admin of that application. But the main focus should be ACS/OpenACS.
Anyway, I think not mentionning OpenACS at all is a mistake from the description! :).
Regarding the Greenpeace Planet... Well, it's a constellation of websites running on top of OpenACS/Oracle. It is being developed at this stage and should be released during June 2002. I can't tell you much more than this at this stage, except that it's going to be multilingual and should grow a lot during the next few years!
