Microsoft Knowledge Base Article 921914 contains the following summary:
This article applies to the version of Microsoft Windows Genuine Advantage (WGA) Notifications that is distributed during the pilot program. For example, this version is included in the pre-release version that accompanies the Microsoft Software License Terms. To safely and easily uninstall the pilot version, you must install the general release version of WGA Notifications. If you do not install this version, you can follow the steps in this article to disable or uninstall the pilot version.
Important These instructions have not been tested on the general release version of the WGA Notifications. Therefore, these instructions are not supported. Microsoft will offer the general release version of WGA Notifications to users who uninstall the pilot version at a later date. These users will obtain the general release version through the Microsoft Automatic Update service. WGA Notifications is part of the Windows Genuine Advantage program.
When you use a non-genuine version of Windows, you receive a message when you log on that states that the copy of Windows appears to be non-genuine. Then, you are directed to the WGA Web site to learn more. If you do not want to obtain a genuine copy of Windows, you receive periodic messages that notify you that the copy of Windows appears to be non-genuine.
Note If you are running a genuine copy of Windows and want to use WGA Notifications, you may receive messages to update Windows XP.
Regardless of genuine status, users are not denied access to critical updates. However, users who have not validated their computers as genuine are not able to install other updates such as those for Microsoft Internet Explorer 7.0 and Microsoft Windows Defender.