How do I change the nav portlet?
What I want to do: Change the navigation portlet so that only the current top folder and its contents appear.
Go to the ZMI in Plone.
Go to portal_properties → navtree_properties
Put the “topLevel” equal to 1.
Source: Plone Users mailing list archives http://lists.plone.org/pipermail/ui/2006-July/000349.html
Someone also posted a howto in the Plone forums: http://plone.org/documentation/how-to/creating-a-flat-nagivation-portlet