Microsoft has quietly released pre-beta code for Windows XP Service Pack 3 and Vista Service Pack 1, but continues to remain vague about when the finished upgrades will be released.

The company confirmed yesterday that it has released preview code for both updates to testers, but would not say directly when either will be released in their final versions.

While Microsoft said it will have a beta of Vista SP1 available "sometime this year," it won't commit to a firm date. Some insiders had expected a beta to be available by now. As for Windows XP SP3, Microsoft said it is shooting for the first half of next year, but called that date "preliminary" and declined to disclose more details.

A third service pack for XP, which has been in the works for some time, may seem moot now that Vista has been available to consumers for about seven months and to business users for nine. However, there are many XP users, particularly business customers, that would find a third service pack valuable, said Samir Bhavnani, a research director at Current Analysis West.

"A lot of businesses will run XP for a while before they migrate," he said. "I think people always underestimate how much testing is done before someone upgrades to a new generation OS. Many of Microsoft's best customers won't use Vista for years."

That said, Vista SP1 also is an important release for spurring business users to upgrade to the newest OS, Bhavnani said. "SP1 is a very big mental hurdle to clear," he said. "SP1 will get a lot more businesses to adopt Vista than the version that exists today."

Bhavnani deemed the latest test versions with minor developments, but said that they do show some progress on Microsoft's part to get the service packs out the door. On the other hand, they also stir up more anxiety among Windows users about when the next service packs will be available, he said.