Hi
There are lots of different Visa options for moving to Australia - in your case you could possibly go for the Business Visa.
You should be able to get all the information you need here:-
Department of Immigration and Citizenship
But in answer to your question.............NO.....you dont always have to have a job before arriving - in fact most people dont.
Good luck with your journey. If theres anything I can help with just ask.
Rach xxxx