If you will be using good quality equipment in the open, away from built up towns, you might have some success. However, if you use one of the cheap "scanners" in built up areas you will probably experience a great deal of interference from various transmitters - pagers, emergency services, local FM stations, etc. Airband is pretty well "line of sight" so you may not hear ground stations. Make sure you have a good antenna, properly earthed to the car to reduce electrical interference..
I am not aware of any dedicated mobile airband equipment here in the UK, apart from expensive aeronautical equipment and other professional gear. Some amateur radio equipment covers the airband but, like scanners, it is something of a compromise situation and far from ideal. Maybe dedicated gear is available in Oz?
Over here it is illegal to listen to the airband so it would be worth checking your own government regulations to avoid aggro with the law!