Definately not a Dept store bike, Centurion was a Bike Shop bike. Although the suspension setup is similiar to the walmart bikes of today, remember back in the mid 90's that was a pretty common design.

Centurion was still going over in Australia, so since you bought in Brisbane it matches there. There seems to be a strong group on a Australian Forum on Centurions, I would recommend seeing if these guys have some info for you.

Centurion Appreciation Society - Australian Cycling Forums - Bicycles Network Australia

As T-Mar stated in the US Centurion never marketed MTB's they were sold under their other brand the Diamond Back. and the Centurion name was dropped in 1990 and the road bikes became Diamond Backs.