The plugin is still (very) alpha, so use it just for toying around at the moment. Everything you need to know is here. For experiments the needed bzr-xmloutput plugin is best installed into the local bzr-plugin folder (“~/.bazaar/plugins”).
Installation of the plugin itself is best done via the update site mentioned at the project HP.
Publishing branches via ssh (or anything else which requires authentication) currently requires preshared keys for there is no username/password-dialog yet.
If anyone out there is willing to get his hands dirty, either by hacking bzr-xmloutput or anything else related to this (hopefully soon) very useful project, I’ll give him a hug.