Start by learning to sail. A basic ASA 101 type learn to sail course would be a good start. Then get David Seidman's book, The Complete Sailor, and get as much time in sailing in various boats and weather conditions as is possible. Taking a class in navigation is a necessity, but learning the sailing skills to get the boat from point A to point B is more important.
Welcome to Sailnet. I'd highly recommend you read this
POST to help you get the most out of sailnet.
Once you get a boat capable of making the passage from the US to Oz, I would highly recommend you spend a period of time working up from daysailing to weekending to coastal cruising on the boat and getting to know the systems and boat as well as possible. It is only at this point that I'd recommend you take the more advanced ASA navigation courses.
Then try some shorter bluewater passages...and work your way up to a Pacific crossing.
Generally, most boats are far tougher than the sailors on them. If you don't build up and prepare yourself, it really doesn't matter whether the boat is capable of making the journey or not.