I do not think you will be happy with the POT command.

You may want to look into using an ADC. Use one with a 10 bit resolution. This will give 1024 steps on full scale.
Take a known voltage, run it through a voltage divider with one of the resistors being fixed.
With a little calculating the unknown resistance cane be found.

If you need ideas go here
http://www.rentron.com/pic.htm
Examples for using the ADC on a few different chips, and methods.