Despite voluble protests from users, Microsoft will stop selling Windows XP after today – and users will be forced to buy the Vista operating system.

The last trickles of Windows XP will still come through on computers already in stock, but no new copies of the operating system will be sold on new systems after today.
After that, all new computers will be sold with Vista and users will have to downgrade to XP if they really can't bear to use the new system.
They will still be able to buy copies of XP from small stores until the end of January. The only computers that will have the "old" operating system pre-installed will be low-cost PCs like the Asus Eee.
Existing XP users will enjoy full technical support until the end of 2009, with limited support in place until 2014.