This installation expects you to already have Bazaar installed and configured (if you already have Mailman 2 installed and followed the Syster's guide to do it, you're likely already set).
Start by getting the latest branch of Mailman from Launchpad. Go to the place you wish to have it installed ($ cd <dir/where/you/want/it>) and type:
$ bzr branch lp:mailman
The current version has a package problem with zc.buildout in Ubuntu which needs to be corrected (this is related to the following bug: https://bugs.edge.launchpad.net/ubuntu/+source/distribute/+bug/576434). Barry at Mailman will fix this by setting up virtualenv instead of using buildout but for the moment this needs to be fixed manually. This is done by typing:
$ sudo rmdir /usr/lib/python2.6/dist-packages/setuptools.egg-info
You may or may not have this directory, if you get a message saying you don't - don't worry about it.
Continue by (re)installing python-setuptools:
$ sudo apt-get install –reinstall python-setuptools
If you have a mailman installation in /usr/local/lib/python2.6/dist-packages/mailman - rename it to resolve a conflicting error (again, this is a bug Barry will fix with the use of virtualenv, letting us have and use more than one installation of Mailman).
$ cd /usr/local/lib/python2.6/dist-packages
$ sudo mv mailman mailman_old
Go to the place you put the code ($ cd <dir/where/you/want/it>) and start the installation by running these commands in order:
$ python bootstrap.py
Mailman 3 is now split so that the web UI and archives are separate projects. Instructions on how to set up the Mailman 3 web UI can be found on the Mailman Wiki: A 5 minute guide to get the Mailman web UI running