The University of Washington has published free, open source software you use to track the location of your laptop. It periodically communicates its location (ip address) to a distributed set of servers (OpenDHT). With a Mac OS X laptop, you can also have it periodically capture and send pictures to those servers.
When you install the program, you will be provided with a complex, unique identifier. You must save that id in a separate location (e.g., a thumb drive). You will need it if your laptop is stolen.
If your laptop is stolen, you would then install Adeona on another computer and run a program to retrieve the location of your laptop. You would then call the authorities to help you get the laptop back.