Automatici Backup of Laptop to a mapped drive on Windows Server

I am needing a backup software with an agent that I can load on multiple laptops that will automatically kickoff a backup to a mapped drive to a Windows 2003 server, when it connects to our LAN. I have several people that work in the field and I want to backup their laptops automaticallly when they come in to the office and connect to the network. Any Suggestions?