I had this "WGA plonked on my computer last week when I tried download Windows media player.It wont uninstall from "add or remove"control panel.
This worked,,,,,,,
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.