A GPS puck is a GPS the size of a hockey puck, which hooks to your laptop, gets the power through the USB port, and works with any reputable plotting program. You don't need to wire up your other, expensive GPS to your computer, just use this !@#$ thing. Got mine off the internet for $100, which included MS street maps (your own version of Mapquest.) Without the software, its $70.
As Dan said, just tape it to the overhead shelf. Works great. The only problem I had was that Windows thought it was a MS ballpoint (whatever that is), and I had to use a software patch to fix that.
Boris