It's unsecured debt - the banks could technically go through the courts to have the assets sold, but if you are genuine and explain your situation most will behave with decency and accept payment arrangements.
They review them every 3 months but it's usually just a quick phone call to ask if your situation has changed and if you can increase payments at all - keep them on your side by increasing repayments even just by $5 or $10 every 3 months.
Make the payments as low as possible to start off with - AMEX accepted $5/month on an $11000 debt, NAB $20 on a $21000 debt, CBA and Citibank $10 on $7000 debts.
The other thing I should mention if anyone has a big tax debt - just fill out the form 'application for release of debt' available from the ATO website - you need to be able to prove you are in genuine financial hardship and that being released from the debt will benefit you ie prevent bankruptcy.
