I had to use the 3.3v pin as when I connected the potentiometer to the 5v pin the Arduino shut off. So I am assuming that the usb does not supply enough voltage. Also from the Arduino tutorial on http://arduino.cc/en/Tutorial/ReadAnalogVoltage shows that when using a 10k ohm potentiometer you would use 1023 to divide the voltage by.
Thanks for the help.
Stephen