When you create the checkout with the wizard and enable the PayPal Express Checkout option it should put in a link on your checkout page, so if the user clicks on this link rather than entering their info and submitting the order it should take them to PayPal.
When the pages are created like pp_confirm and the other pp prefixed they will contain your credentials that were entered into the wizard.
As for the URL that you are using I don't know if it will work with the .au domain, I think you should try to use the .com domain. Post back and let us know what you discover and how it works for you.