This is from today's "Wired" about Windows XP.

Here's how it works:

After you buy your shrink-wrapped copy of Windows XP on a chilly October night at midnight and you go home to load it up, you'll still be asked to enter a multi-digit "product key" located on the back of your CD case.

But after a month, Windows will present you with a 50-digit "installation ID," with which you're to "activate" your system.

"What you have to do is phone the call center and tell them this code," Lopatic said. Once you do that, the nice people in Redmond, Washington, will allow your computer to go on.