for US cars, it is on the passenger side just above and to the left of the blower motor
This picture (which keeps uploading upside down even when I flip the image in the uploaded file) is taken from the right side floor looking up with the glove box removed on an 03S. Since the photo keeps flipping, the top of the photo is actually the floor of the car.
The following picture shows the heater box out of the car, the red box is the resister pack
