1.Lauch Windows Task Manager.
2.End wgatray.exe process in Task Manager.
3.Restart Windows XP in Safe Mode.
4.Delete WgaTray.exe from c:\Windows\System32.
5.Delete WgaTray.exe from c:\Windows\System32\dllcache.
6.Lauch RegEdit.
7.Browse to the following location:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon\Notify
8.Delete the folder ‘WgaLogon’ and all its contents
9.Reboot Windows XP.
Sources:www.sapost.blogspot.com