The first thing you need to know is that it's going (including your stay in Oz) to take several months out of your life and to cost you a great deal of money.
For example, one cargo service goes from Tilbury to Brisbane via Rotterdam, Dunkerqu, Le Havre, New York, Savannah, Kingston, Manzanillo, the Panama Canal, Papeete, Lautoka and Noumea, taking 43 days. It then takes a further 2 days to get to Melbourne and another 2 before it arrives in Sydney. The fare is charged at €120 per day. So that makes the one-way fare to Sydney work out at €5640. The return leg (from Sydney) takes 38 days, costing €4560, making the total fare €10,200 (approximately £8,400):
http://www.freighterv...0Australia/BCM-01.htm
There are a very limited number of alternative freighter services
http://www.cruisepeople.co.uk/col.htm
but none of them will leave you that much change out of 10 grand. It would probably be cheaper to book two separate cruises and to just travel on the outbound journey of one and the return journey of another. Even so, there hardly any cruise ships that travel that far (because very few people can afford the time and expense involved in such journeys).
I assume that flying scares you. In reality your cheapest (and possibly only) option might be to book yourself onto this course
http://www.flyingwithoutfear.info/
and then to sit back and enjoy the flight to Oz.
Chris