Remove Windows Genuine Notification

First Method
Lauch Windows Task Manager.
End wgatray.exe process in Task Manager.
Restart Windows XP in Safe Mode.
Delete WgaTray.exe from c:\Windows\System32.
Delete WgaTray.exe from c:\Windows\System32\dllcache.
Lauch RegEdit.
Browse to the following location:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify
Delete the folder ‘WgaLogon’ and all its contents
Reboot Windows XP.
Note: With this method, you may be prompted to install WGA Notifications again which can still be unselected.

Second Method
Another alternative suggested by dman is by using System Restore to restore the PC to a previous restore point that WGA Notifications hasn’t kicked in, and then carefully stop KB905474 from been applied to the system. To use System Restore, go to Start -> All Programs -> Accessories -> System Tools -> System Restore.
Note: Again, you may be prompted again to install WGA Notification, so it must be bypassed.

Third Method
This method involves using a cracked version of LegitCheckControl.dll to replace the original copy of LegitCheckControl.dll, and thus bypass the WGA validation and make Microsoft believes that your copy of Windows is genuine. To get rid of WGA Notifications warning messages, the patched version of WgaLogon.dll and WgaTray.exe to replace the existing files.
To apply the patch by replacing the files manually, try to end the respective processes in the Task Manager before deleting the existing files. Most likely is you will have to restart your PC in Safe Mode in order to replacing the original copy of LegitCheckControl.dll and related files. However, there has been automatic updater and even cracked WGA installer that automatically apply the patched version of WGA files.