If you cannot insert a Bzr hook in the server, you can use the Bzr Poller. To
contrib/bzr_buildbot.py (see Contrib Scripts) somewhere
that your buildbot configuration can import it. Even putting it in the same
directory as the master.cfg should work. Install the poller in the buildbot
configuration as with any other change source. Minimally, provide a URL that
you want to poll (bzr://, bzr+ssh://, or lp:), though make sure the buildbot
user has necessary privileges. You may also want to specify these optional
bzr_buildbot.pySHORT or FULL to get the short branch name or full branch address.