Unless you have a special skill that is in demand that cannot be filled in Australia, forget being sponsored. (As in company in Australia does all the paper work). As it appears you have a CPL (JAA) then you won't get sponsored into Australia.
Note, you can only convert like for like, theory papers passed mean nothing.
So, if you hold a CPL/IR with ATPL subjects passed, you will be able to convert to a CPL & IR.
The CASA ATPL exams are a bit different to the JAA ones. For starters, you'll have to convert your CPL first before doing the ATPL exams. Have a scratch around the links provided above as to what you'll need to do to convert your CPL/IR. (Some bridging papers, an IR paper and some flying + medical)
The ATPL theory is such fun. Not. Remember all those JAA papers? Well, they squash them into 4 papers. Sounds easy? Not really. The depth of knowledge required to pass the CASA ATPL is much deeper than the JAA ones. The JAA ones have more "useless" knowledge...
Good luck.