Mary,
I suppose that if you want to know advantages of Zope over OpenACS, then you've got the wrong forum :) (and a wrong web site all together).
If I remember general advocacy POV that can be distilled from various threads found in forums of *this* site, "Zope is a mess." This maybe an oversimplification (by far).
Advantages or disadvantages are a very difficult thing to juddge -- you can't really have a one-size-fits-all. Tell us more about what exactly you are looking for (a full-blown intranet system with all the bells and whistles, or something a lot more down to Earth?), and then you are likely to get a much more up to the point answer.
