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.
I would like to sail sum blue water passages too. I read alot and sail the Bay. Just wanted to suggest reading a true story called " Ten degrees of Reckoning " by Hester Rumberg. Gives you alot to consider.
What worked for me was read, read, read!!!!!
At the same time you do need to do some courses and learn how to sail.....Remember that ' a journey of a thousand miles starts with the first step". So take it, book yourself into a learn to sail course, buy a bunch of books and get into it!!
Get yourself a small sailboat and sail it every chance you get, reading and classes will reinforce what you learn through experience. What’s great about sailing a small sailboat is anybody can buy one, put it in the water and go. A used car top sailboat would be fairly inexpensive and easy to learn to sail through trial and error. With your life preserver on and a tiller in your hand those far off adventures you dream of will no longer seem unattainable.
I agree with adru. You really need to get out and actually sail. Take the ASA lessons - or, at minimum, look on craigslist in your area to see if there are some day charters that are also lessons, and/or crazy dudes that rent their boats out to strangers. We actually had a dude at our marina that did just that. You'll find a way.