Windows Anytime Upgrade (or WAU) make it convenient for customers who’s PC needs may change over time to need a higher edition of Windows 7. There’re a couple of specific situations where WAU will prove useful:
   

Windows 7 Starter to Windows 7 Home Premium: $79.99
Windows 7 Home Premium to Windows 7 Professional: $89.99
Windows 7 Home Premium to Windows 7 Ultimate: $139.99 *(You’ll note that we’ve reduced the price of moving from Home Premium to Ultimate 12% in the US as compared to Vista pricing)

After Windows 7 is released to market on October 22nd, you’ll be able to buy a retail package that contains an upgrade key at a store near you for any of the 3 paths highlighted above. Whether you buy a WAU retail package from a store or online directly within Windows 7, the upgrade takes as few as ten minutes. This’s because it only requires an upgrade key (no media). Your current programs, files, and settings will remain intact. For a rundown of the Windows Anytime Upgrade experience, click here.

Windows 7 Family Pack consisting of Windows 7 Home Premium for installation on up to 3 PCs, and’ll be available starting on October 22nd until supplies last here in the US and other select markets. In the US, the price for the Windows 7 Family Pack’ll be $149.99 for 3 Windows 7 Home Premium licenses. That’s a savings of more than $200 for three licenses.

Source:→ Windows Blog