Creating Users And Groups
Users can be setup and configured under [Start] - [Programs] - [Active Directory Users and Computers]. Make sure that you also assign dial-in rights for VPN or terminal services (or perhaps not) as well as assign the correct groups.
You should create groups before anything else in order to organize permissions hierarchically right from the start. In the ideal situation, permissions would only be assigned to groups and not to individual users. Personal folders are of course an exception.