Microsoft (MSFT) announced it is letting upgraders pre-order its upcoming Windows 7 operating system for as little as $49.  Current Windows XP and Vista users will be able to order the software for half price beginning Friday.

The software company said users can pre-order an upgrade to the Home Premium version and the Professional version for $49 and $99, respectively, while supplies last or until July 11, whichever comes first.

Participating retailers will have the OS available for pre-order or the users can purchase directly from Microsoft with the option of downloading the software directly rather than waiting to receive a physical copy of the installation DVD.

Windows 7 is set to be released on Oct.22.

Microsoft has said the standard pricing for Windows 7 upgrades will be $120 for Home Premium, $200 for Professional and $220 for Ultimate.  The full versions will cost $200, $300, and $320, respectively.

Microsoft’s announcement comes just two weeks after Apple (AAPL) announced a $29 upgrade price for its upcoming Snow Leopard OS at its 2009 Worldwide Developers Conference.

See our Microsoft page for the latest news and videos on the Windows maker.

Users of Apple’s current version of OS X, Leopard, will be able to purchase Snow Leopard for the lower price.

Asked how much Snow Leopard would cost for users of older versions of OS X, including Tiger, Apple spokeswoman Monica Sarkar said a Mac Box Set, which includes the new OS bundled with iLife '09 and iWork '09, will be available for $169.

Typically, releases of Mac OS X have gone for $120.

In addition, the company's Up-To-Date upgrade package will allow all customers who buy a new Mac computer from June 8 until December 26 to obtain the new OS for free (well, at least after $9.95 shipping and handling).