What you should know before installing Windows XP SP3

After a week-long delay to take care of a last-minute compatibility bug, Microsoft Tuesday gave the green light to Windows XP Service Pack 3 (SP3).

The service pack, undoubtedly the last for the aged operating system, was released Tuesday to Windows Update as an optional upgrade, and standalone executables were added to Microsoft's download servers.

To paraphrase -- and, at the same time, contradict -- Winston Churchill, although this isn't the end of Windows XP, it's certainly the beginning of the end. But we come not to bury XP, but to praise it -- and to answer a few last-minute questions now that it's really, truly, yes-indeed available to anyone who wants it.

Can I really get Windows XP SP3 now? Yes. You can grab it from Windows Update (WU) or download a standalone installer from Microsoft's Web site.

Will Windows Update automatically download and install XP SP3? Not yet. Instead, you must choose "Windows Update" from the Start Menu, then click on either "Express" or "Custom." In both cases, WU will offer XP SP3. In fact, it will offer SP3 before any other update or patch.

To start the 30-minute process, click the "Install Updates" button.

Microsoft has said it will flip the switch for automatic download and install -- the setting that most users have ticked in WU -- sometime this summer. Others have speculated that the push date has already been slated for June 10.

Where's the standalone installer? As is its policy, Microsoft has also posted a much larger installation file that doesn't require WU. The XP SP3 standalone installer, which weighs in a 316MB, can be found here .

Anything I should know before starting the update? You could just jump into the fray, but Microsoft has a whole list of steps it recommends prior to installing XP SP3. The list talks about prerequisites and hard disk requirements, mentions (but doesn't recommend) disabling anti-virus protection and suggests several other moves, including making a full backup before you begin.

That document is also a good resource, or at least a good starting point, for troubleshooting a balky XP SP3 update; it includes information on a host of potential error messages.

You also need to uninstall any now-obsolete release candidate or beta of SP3 that you've stuck on the system. We covered that in an earlier FAQ under the section "Do I need to prep my PC for the final version of SP3 if I've installed one of the early versions?"

Anything else? Yes. Microsoft has warned users of Internet Explorer 7 (IE7) that they won't be able to easily revert to the older IE6 once they've upgraded to XP SP3. And in other browser news, the company's also told users who have installed IE8 Beta 1 that they won't be seeing SP3 on Windows Update.

To do otherwise, according to a long post to the IE development team blog, would invite stability problems.

Microsoft recommends that users who want to retain the ability to downgrade from IE7 to IE6 should uninstall the former before upgrading to XP SP3. Once Windows XP has been updated to SP3, users can then install IE7 and if necessary, later restore IE6. IE8 Beta 1 users should also uninstall the preview before upgrading, Microsoft says.

Why did Microsoft delay rolling out XP SP3 for a week? The company said it had only recently discovered a compatibility bug in the retail point-of-sale software it sells to businesses that cropped up in XP SP3 (and also the newest version of Windows Vista , SP1). As a result, it postponed the expected April 29 release date.

According to a message posted to the support forum for Microsoft Dynamics Retail Management System (RMS) on April 24, the company had identified problems, including data loss and corruption, when the software was run in Vista SP1. Only after it announced XP SP3's delay, however, did Microsoft confirm that the same bug affected RMS when it was installed on a PC running XP SP3.

Once Microsoft had created and deployed filters to WU so that machines running RMS would not be offered the XP SP3 update, it cranked up delivery.

What's new in XP SP3? As we've said before, not much. It does include a few new features, however, which are spelled out in this overview. The biggest change, at least in terms of the number of users it will impact, is the modification to product activation. New installations of Windows XP SP3 will give users the same 30-day grace period currently offered to Vista customers before they're required to enter a product activation key.

The change is only for new installations and doesn't come into play if you upgrade from SP2 or an even earlier edition of XP. If you're just updating, you shouldn't be asked for a product key.

What's been fixed in XP SP3? Lots, according to the official list that Microsoft published. The list, which you can view here is long. By our count, the service pack contains 1,174 individual patches and hotfixes, essentially every one that Microsoft's issued since it rolled out XP SP2 in 2004.

And the list is remarkably up-to-date. For example, the most recent security patch that applies to Windows XP -- MS08-025, a fix for a flaw in the kernel that was issued April 8 -- is included.

What if I have problems upgrading to SP3? Normally, Microsoft refers users who obtained XP as part of a new PC to the computer manufacturer or reseller when problems pop up, or charges $59 per support request to answer questions. But as is its practice with service packs, Microsoft will provide free support for any XP SP3 installation or compatibility issue. You can reach support free-of-charge by telephone, e-mail or real-time chat.

The place to start is this XP SP3-specific page on Microsoft's Help and Support site.

Will XP SP3 be available at retail? Nope. Microsoft confirmed today that XP SP3 will not be shrink-wrapped for store shelves. "Windows XP SP3 is available to OEMs as an option for some of their product lines [and] for Volume License customers to simplify maintenance of their Windows XP machines," a company spokeswoman said after noting that others won't see SP3 as a separate product.

That means you'll have to do an after-the-fact update to SP3 on any newly-purchased-and-installed copy of Windows XP.