Paul,
As someone who had never flown in Oz prior to starting my Command Multi IR, had about 2000 hous flying IFR in the crappy east coast WX you get here in the US and was used to the extremely simple approach the Yanks take to alternates and IFR flight planning. I have to say, that the IREX was by far the hardest exam I've ever taken. A complete sh!t in fact.
Do yourself a favour, find yourself an experienced Ground Instructor and spend the cash on a quick course. I did some ground school with Martin at FTA at Archerfield. Best $600 I've ever spent. Walked out only dropping one question.
Good luck.