The MoinMoin wiki has to be where documentation goes to die. I've never worked with a piece of software that has such crummy docs, everything is half done etc.. It makes a strong argument towards never using a Wiki for documentation.
Anyways, here's my recipe to get HTTP Digest authentication working with MoinMoin on apache2. It wasted some of my time to get it all right, so hopefully this helps someone since the docs won't.