run a startup script before the user login

Hi

I try to run a system script on a commuter, before the user login.
The script change the user password.
I need that the script will run before the "Windows Authentication dialog"
appear (before the user can login)

On Win 2000 I put my script in the group policy, in Windows Settings ->
Script -> Startup
In addition I set these settings:
Run logon scripts synchronously Enable
Run startup scripts asynchronously Disable
Run startup script visible Enable

This works fine. My script is running before the "Windows Authentication
dialog" appear

The problem is in WIN XP SP2, with the same settings, the "Windows
Authentication dialog" appear before my script run.
The "Windows Authentication dialog" appear and after 10-20 sec my script is
running (The user can login before the script so his password is not change)
what can I do to make my script running before the "Windows Authentication
dialog" appear ?

Thanks