Microsoft has announced that, for a limited time only, Windows 8 Pro upgrades will cost just $39.99 via download, or $69.99 for a boxed DVD from retail outlets. Download customers will be able to buy a backup DVD for $15 plus shipping and handling.

Between its launch—whenever that will be—and January 1st, 2013, users of Windows XP, Windows Vista, and Windows 7 will be able to buy the cheap upgrades to Windows 8 Pro. Windows 8 Pro is the higher of the two mainstream Windows 8 SKUs, and it includes features such as BitLocker, Hyper-V, and the ability to join Windows domains.

The new Windows 8 pricing undercuts the equivalent promotional pricing for Windows 7 upgrades. During the Windows 7 promotion, upgrades to Home Premium and Professional were available for $49 and $99, respectively.

In Windows 8, the Media Center product is separate from the main operating system, and buyers of new systems will have to pay for it. Anyone upgrading with this promotion will, however, be able to install the Media Center add-on for free, avoiding the forfeiture of features that they currently use.

Only Windows 7 users will be able to upgrade their entire operating system in-place, with applications, settings, and data all preserved. When upgrading from Windows Vista, only settings and data will be preserved. Upgraders from Windows XP will only keep their data.

For those not upgrading, there will be Windows 8 and Windows 8 Pro System Builder versions. Redmond has not yet disclosed pricing or availability for those however.