I want to set up a site for collaboration and discussion of common issues.
I would like to have some parts restricted access, and others free.
I don't want people to have to enter formatting codes just to enter simple text,
but still I want it to be able to display html links in the text that users have added,
like it is in this forum, and maybe also pictures.

I have found that there are a small handfull of options of the various kinds out there, but
what is the easiest to set up that still fulfills the criteria??

It seems that the wikis are more difficult for the user, so I'm kind of drawn to some other solution.

If it just for discusion why not just use a forum such as this one which is
vBulletin, or invision board. I have a invision board site and it is fairly easy to use and has all the features you are asking about. Once you install it to the server most 90% of the board settings are done through an admin gui.
Only major changes occur though the server.

Also as far as CMS goes there is Mambo and also another good one is Plone which is based off of Zope application server.

Also, PHPbb2 is very nice for setting up forums and discussion groups. Just remember to install MySQL first, so the forum software has something to work on. PHPbb2 is very easy to set up. Their web site claims "up in 10 minutes!"

It only took me an hour :>

Edcutis

or extend the phpbb to phpnuke, depends on youre needs ofc

thanks - thats something to get started on