I found this useful bit of information from a helpful bloke in DFAT a few years back; hope it may save someone else some time too, who may need to validate passport numbers.
Australian Passport Numbers do not contain an embedded check digit.
However all unexpired Australian Passports are of the format A9999999 where A is alpha A-Z and 9 is numeric 0-9.
There are always exactly 7 digits.
The letters O, S, Q and I are not used.