What is difference between Registering and activating a genuine software?

Hi, Nehemiah,

In addition to TrekDozier's response:

To continue to use all the features of your product, you need to activate your software. Microsoft Product Activation is an anti-piracy technology designed to verify that software products have been legitimately licensed. It is quick, simple, unobtrusive, and helps protect customer privacy. Product Activation works by verifying that a software program's product key, which you must use in order to install the product, has not been used on more personal computers than intended by the software's license.

Registration is completely voluntary and does require sharing some personal information. Registration will provide you access to special offers and notifications.

Registration is the process of providing information to Microsoft (such as your e‑mail address) to sign up for update information, tips and tools, and other news about Windows. Registration is not required.

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). Product activation makes sure that each Windows XP license is installed in accordance with the EULA and is not installed on more than the number of computers that the license permits.

How To Activate XP:

http://support.microsoft.com/kb/307890