This might not be the best shot but here’s what I did:
Directory_country_region and directory_country_region_name contains the states. I added these manually (not nice) to the db. Now the appear as dropdown when the right country is selected.
I don’t know how to add the suburbs in the same way as this “third layer” is not part of the database schema. Unless you can live with a simple text input you’ll have to take a deep look into how the country state dependency is implemented and do the same for the suburbs in a custom module/extension.
IMHO the eav approach taken for the product configuration also should have taken to all aspects of the customer profile.