Along with the monster patch batch it issued Tuesday, Microsoft Corp. also prepared Windows Vista users with what it said are the last two prerequisite updates they'll need before they can download Service Pack 1 (SP1) next month.

The two updates, which were offered to users via Windows Update -- and will automatically download and install on the majority of machines running Vista -- make changes to Vista's install components. They followed another prerequisite that was delivered last month.

"Both of the Windows Vista SP1 prerequisites are marked 'Important' and will install automatically if you have Window Updates set to the recommended configuration," said Nick White, a Microsoft program manager, in a post to the company's Vista blog Tuesday.

Separately, a Microsoft spokeswoman said in an e-mail Tuesday that "we are offering these prerequisites to simplify the service pack installation and to help our customers avoid additional reboots at installation."

The two updates -- described in more detail by a pair of support documents pegged as KB937287 and KB938371 -- are the final files required before Vista will allow SP1 to install on a PC. The other, identified as KB935509, was pushed to users last month. That update targeted BitLocker, the full-drive encryption technology bundled with Vista Ultimate and Vista Business.

KB935509, however, was caught in a Microsoft snafu last month when it was mistakenly sent to users running Vista Home Basic and Vista Home Premium, two versions of the operating system that don't include BitLocker.

Microsoft confirmed the error, but it said Home Basic and Home Premium users who had received and installed the updates, which never should have shown up on their Windows Update lists, were in no danger.

When the company first offered Vista SP1 to the public in December 2007, it warned users of the three prerequisites and told them that their PCs would reboot after each was installed.

Even Tuesday, however, some Vista users remained confused. "Let me get this right ... you have to update your installation of Vista before you can update it again with SP1?" asked someone identified as "Superpotato" in a comment to White's blog post. "Maybe I'm missing something, but couldn't these requisite updates have been included in the actual SP1 installation file?"

Superpotato then took a shot at Microsoft's Vista SP1 update process, saying, "Sometimes I could swear you guys are actually working for Apple, trying to get everyone so frustrated that they'll switch."

Microsoft typically uses Patch Tuesday -- the label for its scheduled delivery of security patches on the second Tuesday of the month -- to provide users with other updates that it designates as "nonsecurity, high-priority." At times, that policy has created a stir as users object to what they see as a mashup of must-have vulnerability fixes and optional updates.

In November 2006, for instance, Microsoft rolled out Internet Explorer 7 (IE7) to Windows XP users via Windows Update, and the company used XP's Automatic Updates setting to automatically push the new browser. At the time, some users squawked, but Microsoft defended the move on security grounds.

It made no similar attempt to justify Tuesday's delivery of the two final prerequisites.

Although Microsoft announced last week that it had wrapped up work on SP1, it will not give most users the chance to obtain the update until mid-March. That decision, company executives have said, was based on problems with hardware device drivers that it hopes to solve or at least quantify in the next few weeks.

Users have blasted Microsoft over the delay, especially IT professionals and developers who have paid hundreds to subscribe to TechNet Plus or MSDN (Microsoft Developer Network), both which tout early availability of updates as a key benefit.