When no pressure is placed on the pedal, you'll read about 20 KΩ. When pressed down all the way, you'll read about 1 KΩ, and the resistance change is linear with the motion. Connect one side to ground, then the other side to a 10K resistor pull-up to your microcontroller's logic voltage. Then read the divided analog voltage, like you would with a photo-cell or other 'resistive' type sensor.
The top of page 4 [u]here[/u] shows you how to wire a photocell (or other variable resistor) with a regular fixed-resistor in series to make a variable [u]voltage divider[/u].
Except, the junction of the two resistors can go directly to the Arduino's analog input (no amplifier required).
Note that although the variable resistor is linear a voltage divider depends on the ratio so the output voltage is not linear.
Or, there is probably a regular potentiometer inside so if you can easily get it apart you should be able to bring-out all 3 wires and you can use it just like the [u]Analog Read Serial Example[/u], and that will be linear.