turning my Macbook into a gps

I do a lot of long and short distance train travel. Quite often I wonder where the heck am I. So the question is what is the best and or least expensive way to turn my Macbook running 10.6 into a GPS unit.

Thanks in advance for any and all help.

There are two applications out there that are considered the better of the lot,
RouteBuddy › Maps for Your World
MacGPS Pro Mac OS X Navigation Software - Home

With both you also need to buy maps (These are almost always application specific so forget using MacGPS Pro maps in RouteBuddy) for your region and a compatible USB/Bluetooth GPS unit which are usually listed on the developers website.

Thanks for the reply and I will investigate both.