the extension can be downloaded under http://blog.pagansoft.de/download/accesscontrol-0.3.zip
The new version is tested on MediaWiki 1.7.1.
Here are the changes for version 0.3:
- access is now also controlled for editing the pages (if you access it manually per action=edit in the URL)
- only sysops can now view and edit the “Usergroup:..” pages
- added a changelog
- added an entry on the extension page on MediaWiki.org
My original article with the last version can be found here.