Stomper has the right idea here, get copies of all your mortgage docs. from banks, mortgage brokers RE agents etc. including e-mails etc., what your looking for is for written evidence like "property prices double every 7 to 10 years" "property prices never go down" "risk free" that sort of thing of you not understanding risk, as clearly you didn't understand the risk you were taking.
THEN once you understand how you got into this mess see a lawyer, [most lawyers will give you the first visit for free] and you may have to research the right lawyer, don't be put off if the first lawyer isn't keen, this will be a growth area over the next few years so see how you go.
Good luck and remember if the risk wasn't explained to you particularly by your mortgage broker who should have been acting in your interests then you may have grounds for recourse from other parties.
AND those properties in Qld. may not have bottomed yet, they may have further to fall, I haven't seen that mentioned here yet,
Very poor advice