If you're having trouble setting up Team Project user permissions through the Beta 2 UI, try dropping to the command line and using gssutil.exe, it has a bunch of command line help that should get you mostly on your way, the /g+ option will let you add a user to groups.  Another tip to watch out for - the project name gets surrounded by brackets, for example if the project name is Adventure Works the command line would be /g+ "[Adventure Works]\groupname