[Zope] Plone not installing on Zope

Hi: I installed Zope 2.8.4 and moved all folders from the untarred Plone 2.1.1 download to the Products folder of the instance of Zope I'm running in my home directory. I have Python 2.3.5. However, as the Plone installation instructions mention, "Plone Site" does not show up in the drop down menu of items in the ZMI. I've tried different versions of Plone to no avail. What am I doing wrong here? Thanks Qass