I don't have personal experience, but my MIL and her sisters have just been through this with the property they inherited from their parents. A quarter acre block in an inner Melb suburb with an old house on the front. They subdivided, had plans for a second house drawn up and approved by council. They whole process took them about 8 months but is now worth at least $100k more and they didn't have the hassle of building the second home. I think they only paid a few thousand in fees and plans.
I would look at the area first. What is the average block size, and are other people in the area subdividing? Find out as much as you can from the council and other people in your area.