You will not be able to run some versions of Vista on a Mac, it has been revealed, as the licence specifically forbids its use with virtualisation products.

Microsoft has reworded its End User License Agreement (EULA) to forbid the use of Vista Home Basic and Home Premium Editions with virtualisation products like Parallels and VMware.

“USE WITH VIRTUALIZATION TECHNOLOGIES. You may not use the software installed on the licensed device within a virtual (or otherwise emulated) hardware system,” reads the licence.

That doesn’t preclude Vista Home editions from being installed on Macs running Boot Camp, however, since Boot Camp isn’t a virtualisation or emulation technology - it makes Windows run natively on the Mac. For now, however, Boot Camp is still in beta development, and still officially works only with Windows XP.

Meanwhile, the EULA included with Vista Enterprise and Ultimate editions allows that operating system software to be installed on virtual or emulated hardware systems. "In short, this means that if you’re a user and you want to run Vista virtually, you MUST buy the highest end versions of Vista, or you’ll be in violation of the Microsoft EULA," Parallels complained on its company blog.

"Most customers using this technology are primarily business users addressing application compatibility needs, or technology enthusiasts," said a Microsoft spokesperson. "So virtualization will be supported in Microsoft Windows Vista Ultimate and Vista Business SKUs. Home users have rarely requested virtualization and so it will not be supported in Microsoft Windows Vista Home Basic and Home Premium SKUs."

The issue for users is price: Microsoft sells its Home editions of Vista for $199 or $239, while Business and Ultimate editions cost $299 and $399 respectively.

"To me, this strategy could hold back users who embrace cutting-edge technologies like virtualisation, which means they won’t upgrade to Vista. This means that Microsoft has effectively lost an upgrade customer (in the case of Windows PCs) or an entirely new customer (for Mac and Linux users)," wrote Parallels' Ben Rudolph.