Not changing direction of the thread except this one update for starskate.
FAA ATPL to CASA = Commercial Air Law written exam, then ATPL Air Law written exam. Also need IREX written (Instrument Exam) and MECIR (Multi-engine Command Instrument Rating check flight).
I just went back to Australia last month and got this information from a flight instructor at my old airport.
Refer to casa.gov.au website for full information though. And Airservices online shop for appropriate texts (regs, etc)
Also, see the Aust./NZ forum and search for the conversion and there's several good posts with helpful information too.
I'm looking at doing exactly the same thing, so if you need to PM for any more information, maybe I can help???