User Roles work well but require that you define AD groups for the departments. Not sure why your view is not switching. Probably either the order of the User Roles or the Open Rules.
AD Web service (we sell one for $19.95) also can be used effectively. View switching is trivial. Lots of posts on how to do it and examples in SDK as well as the sample out-of-the-box solutiosn that ship with InfoPath.
Good luck!
Patrick Halstead [InfoPath MVP]
InfoPath Dev Seattle
Patrick Halstead
Project Manager at Qdabra