You bought UMD or downloaded the game ?
If you run a lap in time trial mode, save ghost replay, quit the game, connect to your PC, PSP, SAVEDATA : do you have UCES*****RPLY" prefix or "UCUS*****RPLY" ? If you have UCES -> EUR version of the game, if UCUS -> US version of the game, have you other prefix ?
I don't know if the Australian PSN Store is EUR version or US version (not sure about your "PAL PS Store either"
) but I guess it would be EUR, if you downlaoded EUR SP Model pack with a US game -> won't work, US SP Model with a EUR game -> won't work... Or both of us are the unluckiest guys in the world
!
So the first thing you have to do is to check which version of the game you have or try to download the US and the EUR SP Model pack to compare ! Personaly I have a PSP 3006 bought in HK, downloaded version of the game in EUR PSN Store + SP Model and everything is ok !
Now if you do have a UMD US version of the game but an Australian PSN account with EUR version, you might have to buy another Memory Stick Duo, create a new account on US PSN Store and download the pack on the new Memory Stick Duo. I haven't tried it yet I'm waiting for the US version of the game to be cheaper than that 39.99 dollars like the special offer we had in EUR PSN GTPSP = 17.90 euros (we have Assassin's Creed Bloodlines for 19.90 euros right now) ! So I don't know if it's possible-. However I know that when I download US games demos on the EUR PSN account+Memory Stick, that doesn't work, but works on the US PSN Account+Memory Stick 2, so I think it might work too with the games !!!-...
Here is the EUR SP Model pack :
Enzo Ferrari '02 Giallo Modena
Lamborghini Countach LP400 '74 Arancio
Citroen GT by Citroen '08 Yellow
Nissan GT-R SpecV '09 Metallic Blue
Mercedes-Benz SLR McLaren '03 Red
US version SP Model pack :
Enzo Ferrari '02 Giallo Modena
Lamborghini Countach LP400 '74 Arancio
Citroen GT by Citroen '08 Yellow
Nissan GT-R SpecV '09 Metallic Blue
Bugatti Veyron 16.4 '09 Black
Good luck !