Microsoft are running another Christmas special, this time for Windows 7. Microsoft retail a Windows 7 Home Premium upgrade license (as a download) for AU$199 or AU$221.99 with a disc. There's also an option for Anytime Upgrade from Starter to Premium for AU$140.
At the moment there's a "while stocks last" Christmas promotion, where Microsoft are offering a family pack which can be used to upgrade 3 computers to Windows 7 Home Premium for AU$249. The pack is available from Microsoft's site as well as Bing Lee, Dick Smith, The Good Guys, Harvey Norman, JB HI-FI, Officeworks and WOW Sight & Sound (price may vary).
The pack will include both 32 and 64-bit versions and can be used to upgrade any existing Windows 7 installation to Home Premium. Alternatively, it can upgrade XP or Vista installs to Windows 7 Home Premium also.