Group Policy for User Logoff

I have written a *.bat file that will copy a user’s *.pst file from their local drive to the server so it will be backed up.

I need to implement a group policy that automatically runs this file when a user logs off the network.

Can I do this from the server or do I have to do it at each user station?

Currently running 2K Server with mixed 2K and XP Pro clients. I don’t have a lot of experience with Group Policy.