REDMOND, WA — On Thursday, Microsoft issued a new release candidate of the anticipated Windows Vista Service Pack 1. It was the second build sent to testers in as many weeks, fueling speculation that a final version of Vista’s first major update is imminent.The code has not been made available to the public — yet. However, even though the previous build initially was intended only for an invitation-only group of about 15,000 corporate, consumer, and vendor beta testers, within days Microsoft made it available to the public via its Windows Update service.

The official word from Microsoft is that Vista SP1 is scheduled for release during the first quarter of 2008. Last week, a report out of Taiwan let slip a rumored release date — February 15th — but a Microsoft spokeswoman declined to confirm or deny that when questioned by a reporter for Computerworld.

Also made available to testers last week was a new build of Windows XP SP3, which is scheduled for public delivery within the first half of 2008. A previous build is available at the Windows Update website. Microsoft has been criticized for neglecting the XP service pack in favor of Vista modifications despite XP’s greater popularity with consumers. The company has taken great pains to promote the impending release of Vista SP1’s new features and changes, but little has been said about the details of XP SP3.

In November, Forrester Research Inc. indicated in a report that “Vista’s biggest competition isn’t Apple or Novell or Red Hat: It’s Microsoft itself; it’s XP.”