Hi Torjus,
Google Groups is one way, but there's more than one way to skin a cat.
It depends if you want the forum to be hosted on your own web server or not.
If you wanted to host your own forum, you could use free forum software such as phpbb - this would mean you install phpbb script on your web server, along with a linked SQL database.
Obviously this means you have to do al the db admin, apply mods and patches etc etc (like what Tony does here)
Alternatively, you could use a free online forum setup like
www.createforum.com
This allows you to set up a free forum all through the web, all you have to worry about is deciding how you want it to look and administering user accounts.
I reckon the second route would be the easiest - have a link to the forum from your site, and only allow people into it that you wish.
You could create a broader forum if you wished, covering paleo and primitive subjects and other stuff you're interested in, then have separate restricted sections for courde attendees...