tower,
re converting an Aussie PPL or even a CPL/IR to a JAA ATPL is a very expensive exercise.
If you do not have a FULL ICAO ATPL + CIR then you will not only have to do all 14 JAA ATPL exams but you will have to do the FULL JAA IR syllabus as well ie around 50 hours of flying and the CPL skills test as well. As you can imagine it is costly.
So, to see where you fit in, go to the CAA's website and have a rummage around.