Debt was A$5.1b at 30 June 08. Exchange used to convert debt into AUD was 0.96
Debt now higher because the exchange rate used at 31 Dec 08 was 0.69.
Likewise, US assets will be higher because of the much weaker AUD nothwithstanding any decreases in US property values for the HY ending 31 Dec 08.
Have a read of the announcements CER made on 29 August 2008. It should make it clearer for you.