If you have or do not have a legitimate copy of Windows and if it insists on reminding you constantly, you can stop this by simply removing the WGA reminders with the method described in this tech-recipe.
Remove the non-genuine copy of Windows XP nag screen and the You may be a victim of software counterfeiting reminder.
You will need to start in safe mode.
Use the Task Manager to stop the process wgatray.exe. This will allow you to delete the files giving the nag screens and reminders.
*NOTE: For some versions of XP (home edition), you will need to stop this process before restarting into safe mode.
Delete the file wgatray.exe in both of the following directories:
*This stops the pop-up balloon.
Now, open regedit:
Naviagate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify,
and delete the entire folder called WgaLogon.
Then, restart your computer.
You will be prompted to re-install these services which have been deleted. Simply write down the services it says are missing, and de-select them from the msconfig -> services tab, and they will be gone forever.
If you get the odd pop-up or returning screen, you may also disable the System Event Notification under this same menu.
-William. § (marvin_gohan)