Microsoft senior vice president Bill Veghte announced the next version of Windows, known as Windows 7, will ship in or near January 2010.
The letter, sent to enterprise and business customers, will eventually be publicly posted on Microsoft's Web site.
In the letter sent to "Windows Customers" and titled "An Update on the Windows Roadmap," Veghte said "our plan is to deliver Windows 7 approximately three years after the January 2007 general availability launch date of Windows Vista."
Veghte wrote, "You have told us you want a more regular, predictable Windows release schedule" and he said that was the impetus for setting the 2010 the ship date.
Vista has been slowly gaining steam, but is still drawing fire from critics who say it has not lived up to promises.
Veghte went further in addressing customer concerns over application compatibility, which had been a problem shortly after Vista's release.
"You've also let us know you don't want to face the kinds of incompatibility challenges with the next version of Windows you might have experienced early with Windows Vista. As a result, our approach with Windows 7 is to build off the same core architecture as Windows Vista so the investments you and our partners have made in Windows Vista will continue to pay off with Windows 7. Our goal is to ensure the migration process from Windows Vista to Windows 7 is straightforward."