Acquire Privileges Dialog
Simply check Acquire the privileges of another citizen, enter their citizen name and the privilege password they gave you, and press OK. If the privilege acquisition succeeds, the dialog will go away.
Once enabled, you will continue to acquire their privileges (even in subsequent Active Worlds sessions) until you disable privilege acquisition or they change their privilege password. To disable privilege acquisition, simply bring up this dialog again and uncheck Acquire the privileges of another citizen.