http://support.microsoft.com/kb/905474/en-usCitat:
• Logon notification
When you log on to a non-genuine copy of Windows XP, you receive the following logon notification error message:
You may be a victim of software counterfeiting. This copy of Windows is not genuine and is not eligible to receive all updates and product support from Microsoft.
Click Get Genuine now to get more information and resolve this issue.
When you receive this message, you have the following two options:
• You can click Get Genuine to start the Get genuine Windows process.
• You can click Resolve Later. If you use this option, an icon will be available in the notification area that you can double-click to start the Get genuine Windows process.
How to uninstall Windows Genuine Advantage Notifications
You can use Add or Remove Programs to view Windows Genuine Advantage Notifications, but you cannot use Add or Remove Programs to remove the notifications.
You can temporarily disable Windows Genuine Advantage Notifications. To do this, right-click the Notifier icon in the notification area and select Change Notifications Settings. Then, follow the prompts. This will disable the Notification Prompts until a new release of the Notification Update is released.