Windows XP Service Pack 3 (SP3), the next significant update to the operating system, now won't appear until the first half of 2008, Microsoft quietly revealed this week. In January, Microsoft had promised SP3 in the last half of 2007.

Although Microsoft gave no reason for the delay in its revised Windows Service Pack Road Map, which was updated Tuesday, it effectively pushed back SP3 by at least six months. SP3 for both the Home and Professional editions of Windows XP is now scheduled to release in the first half of 2008. Windows XP's last service pack, SP2, launched in August 2004.

The new schedule means that Microsoft could drop support for Windows XP within months of SP3's release. According to its published support commitments, Microsoft has promised to maintain Windows XP for two years after the release of Windows Vista. If Vista debuts on time in January 2007 and Windows XP SP3 doesn't appear until June 2008, the latter would age out in January 2009, seven months after it was unveiled.

In January 2006, Microsoft announced that XP SP3 would not appear until the last half of 2007, about a year later than most analysts had expected. Microsoft strives to release service packs, which are cumulative collections of past security fixes as well as new features, every 12 to 18 months. In the case of Windows XP, however, the interval between SP2 and SP3 would be 41 months at best, and possibly as long as 46 months.

Some users reacted viscerally to the news. On the Neowin Windows enthusiast site, one user identified as "yakumo" commented: "If that's not some lame a** artificial Vista pushing scam then I don't know what is."

Others bemoaned the number of patches to SP2 that have to be applied to bring a system up to date. "I've just reinstalled actually," wrote someone named "markukcouk." "As of yesterday, if you install XP with SP2 slipstreamed in, you firstly get 2 updates (Windows Installer and WGA [Windows Genuine Advantage, anti-piracy software]) and then a huge 73 critical updates. I dread to think how many updates I'll have to install in 2008 -- and knowing my company, it's not certain we'll be on Vista by then!"