TrueCrypt will not help you. Passwords and decryption keys must be provided if ordered by a magistrate, or you face six months in jail.
The Australian Cybercrime Act 2001 No. 161, Items 12 and 28 grant police with a magistrate's order the wide-ranging power to require "a specified person to provide any information or assistance that is reasonable and necessary to allow the officer to" access computer data that is "evidential material"; this is understood to include mandatory decryption. Failing to comply carries a penalty of 6 months imprisonment.
This has been in place since October 2001.