I have only a little experience with arduino, and none with resistance value reading. I am pretty sure this is possible, but have no way to wire it, or write code...
Wire one end of the pot to 5V, the other end to 0V and the slider to one of the analogue inputs.
Have a look in the tutorials for details on how to dim a LED.
2 of those pins are marked pin 2, they are connected together
they often times add an extra pin for mounting stability (it would wiggle if it only had 3 pins soldered onto a board)
get a multimeter and verify but I bet pin 1 is one end, pin 3 is the other and pin 2 is the wiper (as it has to slide along a track inside the pot for the entire length of the device it also makes the most since to have 2 pins)