Does the voltage on pin#3 in your drawing change or is the change only from the pot position?
Either way a ADC looks like the way to go. The capacitor in your drawing will serve to "dampen" any voltage change (in its range) making Vout smooth.

If you have not used ADC before, take a look here.
http://www.rentron.com/PICX2.htm
http://www.rentron.com/PicBasic/LM34.htm
http://www.rentron.com/serial.htm

If you are expecting large spikes you would set up the voltage divider so that the maximum voltage in would still be a maximum of 5 volts out of the divider.

The ADC is linear. With an 8 bit setup, 0 volts will read 0, 2.5 volts will read 127 and 5 volts will read 255. 10 bit will have a 1024 step range.

If the voltage is never more than 5, say 3 volts. The reference voltage can be set for this and you will still have full scale.