That's what its for. There must be an app note on Atmels site surely ?

The method is similar to the old joystick interface on a PC. You apply the voltage to an RC circuit and measure the time the volts on the C takes to reach a threshold value for the comparator. You need to discharge the C somehow with an external switch, or you arrange the timing to be very fast, but the repeat readout to be very slow and discharge it with a second resistor, through a CPU. pin. You might need a cheap opamp as a voltage follower. Of course the scale is exponential so you will need alittle look up table, but hell we are only talking 255 values if you represented all of them.

Steve