• Product activation reduces a form of software piracy that is known as "casual copying". Casual copying is the sharing and installation of software that is not in accordance with the software's end-use license agreement (EULA).

• Activation is anonymous, and no personal information is required to activate. 

• The installation ID records an association of the product ID to your computer and a confirmation is sent back to Microsoft. 

• You can then use the product key to install Windows on that computer an unlimited number of times. However, if you want to install Windows on a different computer with that product key, you may have to contact a Microsoft customer service representative.

• Activation is required in 30 days from the first day that you start Windows XP. 

• During activation, you can also register your copy of Windows. 
  

The following guides are available:

How to Register and Activate Windows over the Internet

How to Activate Windows over the Telephone