Joomla VirtueMart Shipment Plugin for Australia Post Services
Employs the AusPost Postage Assessment Calculation API - Tested in PAC 1.3 and PAC 1.4 (latest at 21/04/2013).
Supports: Domestic|International, Parcel|Letter, Regular|Express, Registered, Confirmed, and Insured Post.
For multiple cart products: Calculates parcel sizes and splits into multiple parcels where required as per AuPost parcel limits.
The AusPost PAC spec was impressive also and is available via the AusPost Developer Center.
To configure: First enable the plugin in Administrator -> Extensions -> Plugin Manager, then add a new shipment method in Administrator -> Components -> VirtueMart -> Shop -> Shipment Methods.