they ask quite a variety of stuff really, it's trying to judge your personality, communication skills and reasons for doing med in a 20 minute interview. look at the ausmedstudent forums, i think they have some relevant stuff about interviews.
in terms of offers, there are 180 odd local places and this year about 60 internationals, but keep in mind that about 30 or so of the local places are bonded, either to rural or workforce shortage (you get to put in preferences to rank those or exclude any you dont want, eg lots of people only had unbonded in their prefs and thus weren't offered a place).