J,
U can find all the informations about licence conversions on the CAA website @ the following page :
www.srg.caa.co.uk/pld/fcl/fcl_faq.asp
As far as I know an Aussie licence is just another non-JAA licence & won't give U more (or less) exemptions than say an FAA licence, which is probably cheaper to get.
U can still convert a non-JAA CPL to a JAA CPL without having to follow an approved course, but a non-JAA IR cannot B converted to a JAA IR anymore (since 01 Feb 2001).
MF