Confused and angry users are blasting Microsoft on its own Vista blog over the requirements for downloading SP1 (Service Pack 1). And an industry analyst feels their pain.

Last Tuesday, Microsoft released Vista SP1 to Windows Update, giving most users their first shot at obtaining the service pack. Previously, only earlier testers, volume licensing customers, and IT professionals and developers who subscribed to TechNet or Microsoft Developer Network had access to SP1.

But as it added Vista SP1 to Windows Update, Microsoft also spelled out numerous caveats, telling users that there are as many as eight different reasons why they might not find the update in the Windows Update listing on their PC. Among those reasons: any of 31 language packs, earlier installed versions of SP1, various prerequisite updates, and a number of device drivers.

The service pack is being withheld from machines containing one or more of the listed drivers because, as Microsoft put it in a support document, "these device drivers are problematic on Windows Vista-based computers when you update to Windows Vista SP1."

That made an industry analyst wonder about Microsoft's driver testing process. "When Microsoft said there were problems with drivers, I assumed it was some odd scanner or camera or an ancient printer or something," said Michael Cherry, analyst with Directions on Microsoft, a Kirkland, Wash.-based research firm. "But then I saw the list. It makes me wonder what's going on with device driver testing.

"Microsoft keeps saying that there's this vast ecosystem of device drivers, but it appears there's a much smaller number of reliable, well-tested drivers. Because if these drivers [on Microsoft's list] were tested, that calls into question the testing process."

In fact, many of the complaints posted in comments to Microsoft's Vista blog were related to drivers. For example, one user tried to plumb the depths of his PC to determine why Windows Update suppressed the service pack, but gave up.

"I'm not being offered Vista SP1 on my new Dell XPS M1530 laptop. As far as I can tell, I have two pieces of hardware in the problem list, but the driver versions I have seem to be OK," said "markheath," on the Microsoft blog. "So my question is, is there any way of finding out exactly what is stopping me from being shown SP1 via Windows Update? I'm tired of looking at driver versions."

Others were upset at being forced to root through their PCs to find out why they couldn't update. "I have just spent 1-2 hrs figuring out that I have one of the problem drivers hence why windows update isn't offering me SP1," said someone pegged as "scoobie" on the same blog. "Neither is it offering me an updated new driver. In my book that is not a good customer experience and a bit of a waste of my time."

But there were still others who, after identifying a blocking driver, wondered where to point fingers. "I have SigmaTel audio drivers that are in conflict with SP1. Therefore, SP1 is not available to me via Windows Update," said "Fatalah" on the Vista blog. "SigmaTel was purchased by another company, and driver updates are solely in the hands of OEMs now (Gateway, Dell, HP etc.) I do not expect Gateway to update this driver any time soon. When will SP1 be fixed to work with my old SigmaTel drivers?"

Another user, simply dubbed "Russieb," seconded the motion. "No one seems to be addressing the 'problem' drivers, specifically SigmaTel. As Fatalah mentioned any SigmaTel 'driver updates are solely in the hands of OEM's now.' [In my case] Sony don't [sic] want to know, neither do [sic] Microsoft! This is stopping a large number of users from installing SP1. Can anyone help?"

Cherry felt their pain. "I assumed in February that the drivers would be for an obscure bunch of peripherals, not drivers with this kind of usage."

To Microsoft's credit, the company has offered free support to any user with Vista SP1 issues. In several messages posted to the same comment thread as user complaints, Brandon LeBlanc, who identified himself as a Microsoft employee, directed people to the free support Web site.

"You have a variety of options you can choose for support -- all of which will NOT cost you any support fee," said LeBlanc. "I repeat: support for SP1 will NOT cost you anything -- as long as you choose the correct option for support."