Microsoft has told firms to wait until next month for clarification of its roadmap for Windows desktop editions, after the latest delays to the next release left firms unable to plan for the future.

Earlier this month Microsoft said it could no longer give a target date for Longhorn, the delayed successor to Windows 2000 that was initially due to ship this year. It now seems unlikely to arrive before 2006.

"We're working closely with our software developer and hardware partners now and will have much more to tell you at the Professional Developers Conference in late October," said Greg Sullivan, lead product manager for Windows.

Microsoft continues to recommend that firms deploy Windows 2000 even though mainstream support will end in March 2005, when the product enters the Extended Support phase of Microsoft's product lifecycle. This means that firms will have to buy additional support, which may be charged on an hourly basis, according to Microsoft.

The software giant is sending mixed messages to firms eager to standardise their desktops and to plan upgrades. "Customers deploying Windows 2000 Professional should continue these rollouts," said Sullivan. However, he added that Windows XP Professional was designed to co-exist with Windows 2000 Professional in enterprise environments, so firms relying on Windows 2000 "may want to include Windows XP".

Juliet Andrew of IT consultancy Conchango said, "We are getting our clients to go for XP because it's better to go with something that has a [longer] lifetime when updating infrastructure. We do not feel there is any benefit in going with 2000 now, as it has the same functionality as XP."

Andrew added that some firms that settle on earlier versions of Windows experience driver incompatibilities and other problems when installing their chosen software on newly acquired PCs. "PC makers tend to ship machines with the latest operating system," she said.

Firms that have already standardised on Windows 2000 are unlikely to be pleased at the prospect of having to roll out Windows XP as a stepping stone to Longhorn. Cost considerations aside, Windows XP has many consumer-oriented features, such as Microsoft's DirectX graphics subsystem for 3D games, that are unnecessary in a corporate environment.

Sullivan defended Microsoft's decision to repeatedly delay Longhorn, and to cease providing a due date. "The next version of Windows for the desktop is an ambitious release, and it is too early to confirm a specific ship date," he said. "When there is a more concrete schedule, likely around the release of beta one, we will share it broadly."