Microsoft Corp. will offer free or discounted Windows 7 upgrades to users who buy Vista PCs after July 1, according to a Web site that has accurately predicted the company’s moves in the past.

TechARP.com, a Malaysian Web site that correctly named the release-to-manufacturing (RTM) dates for several Windows editions last year, said that Microsoft will unveil a program for Windows 7 that is similar to Vista Express Upgrade, a 2006 marketing effort that provided free or discounted Vista license to buyers of Windows XP in the months leading up to Vista’s early 2007 release.

According to TechARP, Microsoft will allow resellers to purchase Windows 7 upgrade media, which they can then offer to customers who buy a Vista-power system between July 1, 2009, and a date to be determined.

The upgrades, however, would not be shipped to those PC buyers until the general availability date for Windows 7. Microsoft has not set a delivery for the new operating system, and instead has stuck to a broad range of dates, from late 2009 to early 2010.

The Windows 7 upgrade program as spelled out by TechARP resembled the earlier Vista Express Upgrade. In that program, people who purchased Windows XP PCs between Oct. 26, 2006, and March 15, 2007, were eligible to receive free or inexpensive Vista upgrades.

TechARP did not have a closing date for the program, noting only that it was “TBA,” or “to be announced.” The site did say, however, that resellers would be free to specify a shorter eligibility period than Microsoft’s.

Upgrades will be available from Vista Home Premium to Windows 7 Home Premium, and from Vista Ultimate to Windows 7 Ultimate, said TechARP. Buyers of PCs equipped with Vista Business will be able to upgrade to a Windows 7 Professional.

Vista Express Upgrade also used clearly defined upgrade paths. People who had bought a computer with Windows XP Media Center Edition 2005, for example, were offered only Vista Home Premium, while those who purchased an XP Home PC were given Vista Home Basic.

Microsoft and its hardware partners will be hoping for a smoother road to the upgrades this time around. Vista Express Upgrade was plagued with problems, including delays before users received their upgrade discs. In February 2007, nearly a month after Vista hit retail shelves, for instance, users flooded Dell Inc. and Hewlett-Packard Co. support forums with angry messages about the wait.

In 2006 and 2007, PC makers charged a variety of prices for the XP-to-Vista upgrades. HP offered free upgrades, while others, including Dell, charged users $49. TechARP did not have any information on pricing, which would, if the Windows 7 program is handled the same way, be up to the individual makers.

Microsoft declined to comment on the TechARP posting. “We often explore options with our partners for how we offer products, but we have nothing to announce at this time,” a company spokeswoman said Tuesday.

A public beta of Windows 7 is thought to be imminent — perhaps as early as tomorrow, after Microsoft CEO Steve Ballmer delivers a keynote at the Consumer Electronics Show in Las Vegas — but clues on Microsoft’s own Web site seem to point to a release no later than next week.

Leaked copies of the Windows 7 build, thought to be the one pegged for beta distribution, have been available on file sharing sites for more than a week.