Currently, Plogger is only a single-user installation. A ticket has been filed (awhile ago) to create a Multiple User Option and some other users on the site have hacked the code to make it multi-user (but not anything that I've seen for release to the public).
It is high on the priority list for the development at this point, but I think it will be in a future release (not for awhile yet), unless someone has some time to develop this. I hope that answers your questions. :D