Does any web site explain this subject?
You will need a GPS receiver with output via USB port, and an appropriate
mapping app for the laptop. The app would be likely packaged with a
purpose-built receiver. Try Google...
> What do I need to use my laptop as a GPS mapping system.
Some software that can do that and a device that can get the GPS data.
> What do I need to plug into a usb port that determines
> current location and indicates that on some displayed map?
A GPS device. Its generally better to connect it to the laptop using bluetooth.
> Does any web site explain this subject?
Probably.
A few computers have GPS devices in them already. This includes
the iPhones and iTouches to be sold in July.
I own a Delorme unit which consists of a cd and USB antenna. It costs
under $100.00. I use it extensively and love it.
It works well. The larger screen size is great; if you can find a way
to fit it to your vehicle.
I use a 12 volt power supply for the laptop and the GPS draws power thru
the USB port.
I already had all of these components so no additional cost were incurred.