Internet downloads are the standard way for PC users to get software like Web browsers or anti-spyware apps. But two of the most widely used products in the PC world -- Microsoft's Windows and Office -- have eluded electronic distribution. That's about to change.

Microsoft plans to make its new Windows Vista operating system and Office 2007 productivity suite available for downloading by PC users Jan. 30, the day it releases the products to retailers and computer manufacturers. Windows Vista Business will be one of the editions available for downloading, as well as Office Professional 2007.

Microsoft and Circuit City Stores will sell what are expected to be the most popular versions of Windows and Office for consumers and small-business customers on Microsoft's Windows Marketplace site. Downloading Windows won't appeal to most PC users, but it lets the world's largest software company establish an online beachhead for future sales.

"This is the tip of something we think is going to get much larger," says Bill Mannion, Windows marketing director for consumers and small businesses.

Microsoft before now hasn't considered electronic software distribution secure or simple enough for its flagship products, Mannion says. The company plans to offer Windows and Office for sale on the Web using technology called digital locker, which can store license "keys" that customers use to download.

Microsoft also will offer an online upgrade option to Windows Vista at the end of this month. A program called Windows Anytime Upgrade will let Vista owners buy a more expensive version by clicking a button on Vista's Start menu, which connects to a Microsoft site where they can download software keys to unlock Vista features on their hard drives or DVDs.