If you're in Melbourne and you got your license prior to July 2007, you are not allowed to drive a 'high-powered vehicle'. To determine if your car is a 'high-powered vehicle', use the allowed power-to-weight ratio.
125kw / 1000kg.
So if you are driving a stock gross weight R33 GTS-T, the power-to-weight ratio would be about 135kw / 1000kg, exceeding the limit. However, you must also consider other weight; passengers, fuel, etc.
But either way, most cops aren't going to know. With insurance companies? As long as you have the money, they're happy.