Companies running Windows 2000 on the desktop need to start preparing for Windows Vista, or they may find themselves stuck with an older operating system no longer supported by Microsoft Corp., a research firm said Monday.

Corporations using Windows XP, however, are in better shape and can plan for a slow rollout versus the "forklift" migration that's the destiny of Windows 2000 organizations, Gartner Inc. said.

The analyst firm released a research note on Windows Vista to clarify one sent last week that Gartner felt was misinterpreted in the media. The firm recommends that preparations begin soon after Vista ships so deployment can begin in 2008, particularly for Windows 2000 companies.

For those companies, Gartner recommends calling their software vendors as soon as possible to determine when they plan to support Windows Vista, which is expected to ship by the end of next year. For some specialty business applications, vendors can take as long as three years to support a new operating system.

In addition, Microsoft Corp., plans to end extended support for Windows 2000 by mid-2010, which means companies that fail to act in time could find themselves between a "rock and a hard place," Gartner analyst Michael Silver said.

Contacting software vendors soon will get a timetable for planning a migration to Windows Vista, and also places the vendor on notice of the importance of supporting the new platform as soon as possible.

"If (vendors) hear from enough folks, then that's the motivator (to act)," Silver said.

Gartner expects many corporations to take about 18 months from the time Vista ships to test applications, get independent software vendor support, run pilots and perform other migration tasks. Companies that ignore Vista until 2008 won't be ready to deploy it until 2010.

Windows XP companies can handle the migration in a less urgent manner, adding Vista as they buy new desktops and laptops. Handling the migration through hardware attrition can reduce the expense and hardship of installing a new operating system on each PC manually, which is the method used by many organizations.

Gartner recommends upgrading existing PCs with Vista only if the machines have more than half their useful life left.