Joyent is working on an easy script installer for Trac projects. In the meantime, use the standard 'trac-admin /path/to/trac/project initenv' command when logged into your shell account to initiate a new Trac project.
There is one thing to mind here. The recommended way to run and serve Trac projects is using the tracd daemon, and there is a Bootup Action template ready to let you run that process at all times. The template assumes that Trac projects will reside in a /trac/ directory under the home directory of the respective virtual server. So to create a new Trac project, you'd use e.g.
trac-admin ~/trac/myproject initenv
cp /usr/local/share/trac/templates/*.cs ~/trac/myproject/templates/
If you don't do this, tracd will show an initial list of projects, but any attempts to open a project will only yield blank pages.