IMPORTANT NOTE: Think twice before restricting write access to a web or a topic, because an open system where everybody can contribute is the essence of the WikiCulture. Experience shows that unrestricted write access works very well because:
There is enough peer pressure to post only appropriate content.
Content does not get lost because topics are under revision control.
A topic revision can be undone by a member of the TWikiAdminGroup in case it needs to be.