we will import all old data including users.

new user accounts will be created for old users. emails will be sent advising old users to "activate" their account and set a new password.
http://drupal.org/project/user_import

connections to groups/projects/events will be maintained, but permissions will most likely not be set on the old data.

if an imported user required permissions over an imported (old) node then they can ask for it via our permissions system (see next feedback node).