Bringing the car into Switzerland

Hello, From the beginning of 2012 I am moving temporary to Zürich for nearly one year. I would like to bring and use my car during the period of my stay - firstly as a tourist, then on L or B permit after couple of months. The car is registered in Poland, has a valid technical check as well as third-party insurance honoured in Switzerland. Would you kindly answer my question regarding the legal requirements as a car user: - Taking into consideration the short period of my stay in Switzerland - is it necassary to pay the custom duty for the car? (I am the owner of the car since December 2011) - If custom duty is not necessery and the car has a co-owner (50%) visible in the registration card - can both owners (with L or B permits)drive the car in Switzerland? - If the period of my stay is less than one year, do I need to register my car in Switzerland? How the above questions would relate to my girlfriend's car if she's allready on a short-term internship in Zurich? The internship started in November 2011 and ends in June 2012; she is considering bringing her car in January 2012 (she has been an owner of it for less than six months as well). Most likely we will bring one of the cars but we would like to know which option would be more beneficial for us with regard to costs. Thank You very much for your help.