Googling for GPO login scripts and just login scripts returns the following sites. You will have to modify what they have to get what you need, but this will give you the idea...
http://www.petri.co.il/tools.htm
http://www.serverwatch.com/tutorials...le.php/1474241
your script will be extremely simple.. basically you will put this-
echo off
echo "This is what you want to pop up on the screen."
pause
Login scripts are assigned on the Profile tab of a user account in active directory(users and computers) and local users(computer management for a local account). You can also apply a group policy object that will run a login script for all users that you assign. I would recommend going and getting yourself a good WinXP and AD book, and read up on group policy objects and login scripts as both topics are a bit to large to properly cover in this forum.
