ok this is what airstrike just sent me on msn
1. Replacement steering wheels must be not less than 330mm in diameter. If the original steering wheel was designed with a recessed or padded hub, the replacement wheel must be of similar design.
2.Vehicles manufactured after June 1995, which are required to comply with ADR 69/.. (Full Frontal Impact Occupant Protection), may only be fitted with steering wheels certified by the vehicle manufacturer as suitable for that vehicle
3. Steering wheels fitted to passenger cars manufactured after 1970 must not be replaced with any steering wheel which would cause the vehicle not to comply with the energy absorption requirements for steering columns in ADR 10.
thats for vicotria but its pretty much the same around aust.