An influential analyst firm is predicting that the next version of Microsoft Corp.'s (MSFT) Windows operating system will come out even later than Microsoft has already forecast.

Researchers at Gartner Inc. (IT) said in a report Tuesday that they believe Windows Vista won't be broadly available until sometime between March and June of 2007. Gartner is basing its projections on the progress the Redmond company has made in getting test versions of Vista out the door.

In a statement Tuesday, Microsoft said it disagrees with Gartner's views and is still on track to meet its revised released schedule.

Microsoft said in March that it would not release the consumer version of Windows Vista until January 2007, missing the holiday season and potentially dealing a blow to those who make and sell computers.

The software maker has said, however, that it expects to release Windows Vista to big businesses in November.

Windows Vista is Microsoft's first major update to the company's flagship operating system since Windows XP was released in late 2001. Some analysts had originally expected the system to be released as early as early as 2003.

Shares of Microsoft closed at $24.01, down 28 cents, in Tuesday trading on the Nasdaq Stock Market.