Dell, HP and other suppliers are allowing firms to buy PCs that are equipped to run both Windows XP and Windows Vista.
When a company is ready to upgrade to Vista, they are able to reconfigure a machine to the new OS with software already licensed with their purchase.
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Dell says customers can continue to get Windows XP Professional by exercising "downgrade rights" that come with Windows Vista Business or Windows Vista Ultimate licenses with their machines.
The Dell website says, "Dell has the ability to exercise Windows Vista downgrade rights on your behalf in the factory if your business is still reliant upon Windows XP, and you would prefer to have Windows XP Professional pre-installed on your PCs."
Downgrade rights mean that anyone with a Windows Vista Business or Windows Vista Ultimate operating system can downgrade to Windows XP Professional.
Dell is selling machines with XP pre-installed in the factory and at the same providing a disk equipped with Windows Vista ready to run on the same machine.
The option comes with technical support for both XP and Vista, and users are able to revert back to XP if they find the Vista upgrade does not go smoothly in their business.
Customers may use one operating system at any single time. They cannot run both operating systems simultaneously unless an additional license is purchased.
Windows Vista Home Basic and Windows Vista Home Premium do not have this option, as they are not capable of downgrading to Windows XP, said Dell.
The same scheme is being offered by HP and other suppliers.
Microsoft says it might have a re-think on the 30 June cut-off for the wider availability of XP, but it has already extended the cut-off by five months after originally planning a January withdrawal of the OS.