Network "Change Management"

Does anyone know of a Linux utility that can watch the MAC address
tables in Cisco switches and alert admins as to when a new device has
been plugged in?

Basically, we have your standard client network with DHCP. Internet
access is restricted to authenticated users, and so are the file shares.
However, we've had a few instances where people just plug in their
personal laptops which makes me very worried...

Any thoughts/suggestions as to how I can monitor such events in real
time?

Thanks,
-Dave