Monday was theoretically the day that, over protests and despite its popularity, Windows XP was retired as a way of pushing people to adopt the widely reviled Vista operating system before the very Vista-like “next-generation” Windows 7 arrives, supposedly at the end of next year or at least by January of 2010.

It’s an odd kind of retirement. It technically means you won’t be able to get XP from major OEMs like HP and Dell after they run out of XP inventory or from Microsoft under its Volume Licensing program unless you downgrade from Vista Business or Vista Ultimate to XP Professional.

Boxed copies in retail stores will become increasingly rare finds but your friendly neighborhood systems integrator can legally sell XP until January 31, 2009.

And XP Home and XP Starter will be available on the really cheap PCs, the so-called nettops and netbooks that simply everyone will be doing, until June 30, 2010.

Microsoft, which recently released XP Service Pack 3, says that it will continue to provide “security updates and other critical updates” until April of 2014 at which point XP will be a hoary 14-years-old.