Warsaw - Krakow; the best way of travel is by fast train; just over 2.5 hours. You can also travel overnight train from Krakow - Prague. Prague - Vienna is 4-5 hours by train, but frequent. If you hire a car, remember that unless you take it back to where you hire it (Vienna - Warsaw is a long way), it costs a lot of money for a one way hire and you need to pay for parking each day you stay in the relevant city.
Also note that drivers are maniacs compared to Australia in Eastern Europe and the roads, especially in Poland are in notoriously bad shape.