Hi Matt,
Currently there's no way to push a script into each client using the Concentrator, PIX nor Router.
The only way to run scripts is to execute it directly from the client side using the APPLICATION LAUNCHER feature for the VPN client.
You'll need to copy the script into each end-user workstation and configure the vpn client to run the script upon a successful connection.
In the future, Concentrators will be compatible with NAC. With NAC you can restrict network access based on the OS version, type, Antivirus version, name, etc. You'll find more info about this at www.cisco.com/go/nac