Apple's shares surged as Wall Street bet the move would help Apple grow its current worldwide personal computer market share beyond the current range of 3 percent to 4 percent by attracting more business and home users.
"It makes the Mac the most versatile computer on the market," said Tim Bajarin, a tech industry consultant at Creative Strategies.
Apple's new "Boot Camp" software, a "beta" test version available as a free download, lets computer users with a Windows XP installation disk load it on the Mac. Users could then switch between the two operating systems - using only one at a time - by rebooting, a process that could take a few minutes.
Users would have to get their own copy of Windows XP - the home edition retails for $199.
Apple shares rose nearly 10 percent on the news, raising its market capitalization to $57.04 billion - an increase of more than $5.1 billion.
Van Baker, analyst at research firm Gartner Inc., said Apple is removing one of the hurdles it faced in its long-standing battle to win over Windows-based converts.
"Consumers who were thinking about Macs but hesitated don't have to worry anymore about not being able to run PC software that didn't run on a Mac," Baker said.
When Apple introduced its first computer based on Intel Corp. chips in January, the company said it had no intention of selling or supporting Windows on its machines, though it has not done anything to preclude people from doing it themselves.
Apple said Wednesday that stance remains true, yet the new software will ease Windows installation on Macs. The test software will expire and become unusable after September 2007 but Apple said it will feature Boot Camp in the upcoming Mac OS X version 10.5, code-named "Leopard." Apple said it will preview Leopard in August, but it hasn't yet disclosed a release date or price for the upgrade.
"Apple has no desire or plan to sell or support Windows, but many customers have expressed their interest to run Windows on Apple's superior hardware now that we use Intel processors," Philip Schiller, senior vice president of worldwide product marketing, said in a statement.
Indeed, for months, independent hackers have been diligently working on programs to let users of Intel-based Macs switch between the two competing operating systems.
Others, like Chris Miller, an information technology worker at Johns Hopkins University, have been looking forward to a so-called dual-boot technology so he could play PC games on his Mac.
Apple turned to Intel chips, the same ones used to power most PCs that run Windows, after saying its previous suppliers, IBM Corp. and Motorola Corp. spinoff Freescale Semiconductor Inc., couldn't meet Apple's needs for faster, more energy-efficient chips.
But the Intel-based Macs continued to run Apple's own proprietary operating system.
Because Windows is much more dominant, Mac users don't have access to many software programs written only for Windows. The switch to Intel chips lets users load Windows onto a Mac, without the need for emulation software that slows performance. But until Wednesday, the user needed some technical expertise to pull it off.
American Technology Research analyst Shaw Wu described the announcement as a "significant game changer," while Forrester Research analyst Ted Schadler called the move "smart."
"When they opened the iTunes software for Windows, the market for iPods exploded," Schadler said. "And similarly here, they have a great hardware product, but they've been shut off from businesses and consumers who want to run PC programs, and now they have the software that will allow that."
Yet as Apple expands its reach to Windows users, it is at risk of becoming a higher-profile target for hackers, and it potentially opens its machines to viruses that have long plagued Windows users.
The bulk of Apple's revenues still stems from its computers, though its popular portable iPod players grew to account for about a third of Apple's record $13.9 billion in sales in its fiscal year 2005.
Apple may be trying to break down some of the barriers between Windows and Mac systems, but it still does not allow the reverse, keeping its proprietary Mac OS software tethered to its own computers. Earlier this year, Apple even sent legal notices to force Web sites to remove links to information on how to hack Mac OS X software so that it runs on non-Apple machines.
Microsoft welcomed the development.
"We're pleased that Apple customers are excited about running (Windows), and that Apple is responding to meet the demand." Kevin Kutz, a director in Microsoft's Windows Client Group, said in an e-mailed statement.
Microsoft declined to comment further.
Apple shares gained $6.04, or 9.9 percent, to close at $67.21 on the Nasdaq Stock Market, while Microsoft shares rose 10 cents to $27.74 and shares of Intel rose 18 cents to $19.48.