I have not seen anyone been charged with overturning our Government - Hicks is an International Law issue dealing with criminal offences at the International Level, the act was not in Australia so if it were treason, it would not be an Australian offence.
Sedition is much harder, as sedition does not involve the act of overturning, but merely going against the Government at a higher level - as this is a democracy, this is rarely used against someone.