I agree with Diane if you can do a MYOB course it would boast your wages however a lot of the places I've temped have used a wide range of programes so my biggest suggestion is to have a good basic understanding of Myob and you can prob pick the rest up along the way (thats what I did and it wasn't too hard) You can download a test drive of the Myob package at their website this will let you have a little play around with the software so it's not copletely alien.
As for doing courses before you come have a look at the tafe course offered here Cert 3 and 4 in office administration I think they are called (if your not familiar with tafe it's a bit like the old school polytechnic). Look at the skills you would learn doing these courses and then taylor any further study to meet these standards. A lot of companies will ask if you have done or are willing to do your tafe certs (or so I have found) so what I did was draw up a spreadsheet comparing what was offered on the cert 4 and where my study and experience has covered those areas. That way when an employer asked for these qualifications in their ad I attached this spreadsheet to my application showing I could do everything they wanted. This seemed to help because they don't have (or understand) things like CLAIT so it's best to spell it out!
Hope that helps