Hi,
Same case here, My VISA 176 - WA SS , was issued on old passport number , got it changed to new passport number easily .
Nothing to worry about , I had my new passport issued , and just filled in form 929 ,along with old and new passport copies , sent to DIAC and got it changed in around 10 days.
August 11, 2013 sent to DIAC
August 19 , 2013 - New passport number available in VEVO
Nothing to worry about
Plus, also got confirmation from Australian High Commission that , we can travel on both passports , and just to carry confirmation receipt of
Form 929 - Change of details submission.
Cheers
MS