A prematurely published note to Microsoft's professional customers indicated that the software maker plans to release a nearly complete version of its highly anticipated Windows 7 operating system in May. If that schedule holds up, consumers and businesses could get their hands on a final version of the OS as soon as September.

Windows 7 screen shot
(Click for larger image and for full photo gallery)

A memo appeared briefly last week on Microsoft's TechNet Web site revealing that the company is eyeing May for the release of what's formally known as Windows 7 Release Candidate.

"Welcome to Windows 7 Release Candidate (RC) Testing," said the memo, which bore a May 2009 date stamp and which was hastily removed by Microsoft once word of its existence spread through the blogosphere. "We're on our way to Windows 7, and the RC is a great opportunity for IT professionals like you to take Windows 7 and begin testing it in your real environment," the note said.

The memo noted that Windows 7 RC will be available through June and that Microsoft plans to make an unlimited number of download keys available to users who want to kick the tires on the operating system and provide feedback.

If Microsoft is following a timetable similar to that employed for Vista development, then it's highly possible that the company is eyeing September as a release date for Windows 7. The first Windows Vista RC dropped in September 2006, about five months before the final version shipped. A similar, five-month incubation period for Windows 7 RC would point to a commercial release in September -- possibly in time for the critical back-to-school shopping season.

Microsoft needs Windows 7 to be a hit. Vista, the company's current OS, has failed to catch on with mainstream computer users while businesses have shunned it outright. Many users have complained about Vista's hardware requirements, intrusive security measures, and lack of compatibility with older applications.

Windows sales fell 8% in Microsoft's most recent quarter.

InformationWeek has published an in-depth report on Windows 7. Download the report here (registration required).