If you are going to hack an of the shelf lie detector wiring it to the arduino will depend on the specific schematics of the device.
It would be really fast and easy to DIY. I did a GSR sensor some months ago with the arduino following these steps.
you need:
-Copper tape (this can be found at home-depot or B&Q type of shops sold often as "slug tape" or even thin foil might work)
-a 1mega ohm resistor
-jumping wires, etc.
you cut two little squares of the copper tape to attach to the fingers.
one of this terminals will be conected to the arduino voltage trhough the resistor, from this same point you connect another wire to one of the analogue ins.
the other copper tape square will be conected to ground.
the code is pretty much the same as the potentiometer example as far as i can remember.
hope it works