Ways to skin a wiki
You 'd think there'd be more than one way to do this - and that many of them would be easy. Not, sadly, the case. Couldn't get a workable skin on usemodwiki or mediawiki, and wasn't quite getting anywhere with tikiwiki as the whole Smarty thing was definitely *not* the answer.
PmWiki, however, looks like it might be the biz - skinnable by editing templates, and it can have a range of authorisation options from completely open, through various levels of protection all the way to LDAP....