It will vary from state to state but going from NSW to Qld you have 2 options. Deregister and get refund, then get permission to drive an unregistered car interstate. Then apply for registration when you get there - after getting your safety certificate done.
Option 2 is driving it home and then deregistering (have to get refund from interstate), safety certificate or equivalent, apply for registration. All depends how much rego is left really and how much hassle you like to deal with. Check with your local state transport guys. They will tell you specifics for your state/situation. Provided you get someone who has a clue behind the counter.