Microsoft did yet another turn-about this week and opened the newest version of Windows XP SP3 to the public. It's not final, this last service pack, but it's close.

And it's the first time since December that any XP user has been able to take a peek at SP3.

So although Computerworld's resident Windows guru Preston Gralla warned everyone to be ready to be underwhelmed, we're betting that interest in Windows XP Service Pack 3 Release Candidate 2 will be high.

Why? Because as Vista has stumbled, XP has gained new respect. More than one user has already sworn online that he'll give up XP only when someone pries the install disc from his cold, dead hands. Others have announced plans to stockpile XP when it drops off the retail sales list June 30.

So, what's XP SP3 all about? We thought you'd ask that, so here are a few answers to tide you over now. When the upgrade goes final, we'll follow up with more.

What exactly has Microsoft handed over? Dubbed Service Pack 3, v.3311 once it's installed, Microsoft says that this is SP3 RC2 (for Release Candidate 2). By all indications, it's the same build as the one seeded to the closed-set of 15,000 beta testers about two weeks ago.

Where do I get it? Unlike the only other time that XP SP3 was offered to all comers, it's not posted on Download Center as a manual download. Instead, SP3 RC2 is delivered via Windows Update (WU), Microsoft's primary security patch, hotfix and catch-all update service.

To pull SP3 RC2 from WU, however, users must trick their PC into thinking that it's allowed to do that. A small 38Kb file -- this is what you need from Download Center -- hacks the Windows registry by changing a key or two. Voila! You're in.

What's the process like? Long and semi-cumbersome. But hey, it's prelim, right?

After downloading the hack, the first chore is to uninstall any previous version of XP SP3. For most users, that would be SP3 RC, the December 2007 build given to all comers. To do that, open "Add or Remove Programs" from Control Panel, check the "Show Updates" box, then scroll to the bottom of the listing. Select "Windows XP Service Pack 3" and then click the "Remove" button. The uninstall ends with a reboot.

Next, you should run WU to grab any missing security updates. This applies to everyone, but most of all to users who had been running SP3 RC; like other service pack previews, it refused to "see" XP patches. (One Computerworld test system, for instance, that had SP3 RC installed in mid-December hadn't grabbed any updates during the normal January and February patch cycles.) You may need to reboot here as well.

Finally, run the registry hack downloaded earlier, then fire up WU again. XP SP3 RC2 should now appear. It's a 66MB download for most users, but your mileage may vary. When RC2 has been downloaded and installed, the PC does a final reboot.

Why is Microsoft using Windows Update to deliver SP3 RC2? Our guess is that Microsoft's testing the WU mechanism, which will, after all, be the way virtually all consumers and small business receive the service pack when it eventually goes RTM (release to manufacturing).

The company did the same thing with Windows Vista SP1 in mid-January, it offered SP1 RC Refresh to the invite-only testers and told them to grab it using WU. Two days later, it released the same build to the public, again through WU.