gpg --verify petmail-0.2.2.tar.gz.sig tar xzf petmail-0.2.2.tar.gz cd petmail-0.2.2 ./setup.py install # (maybe as root) petmail
That will start a GUI agent, using ~/.petmail/ as a base
directory.
There is some rudimentary documentation on setting up a client contained in the distribution, in a file named docs/client.txt.
The design paper is available which describes the goals and architecture of the Petmail system.
The CodeCon slides, along with the notes/script, are here.