Hi BeckieC,
I agree with Rupert for an extent. You don't need to get membership before you move here, however if you are going to live here for good might as well get the CPA membership as its more recognised here in Australia than the CIMA.
Next important point is you also need a skilled employment assessment to claim points for work experience. The trick is they only award points for post qualification work experience. From your earlier post I gathered that you are a recent graduate and if CIMA is the only Accounting qualification (unless you have a previous qualification in Accounting) claiming points for your entire duration of work experience would not be possible.