How to interface with an infrared receiver

I ordered some of these:

http://www.goldmine-elec-products.com/prodinfo.asp?number=GP23

There are several infrared LEDs in here that I can see work with my digital camera. There are some (I'm assuming) infrared receivers also. They're two pins but I have no idea how to interface with them.

Are they normally open and when they see infrared they close? Is it a resistance thing like a photoresistor? How does an infrared receiver act?

A two pin IR detector can either be a photo diode or a photo transistor. One way of connecting them up is to put one end to ground and the other to the input (normally analogue input) with a pull up resistor of 100K.

Eventually, your circuit should be fine to drive a digital input on the Arduino... but while you are trying to get everything right, use a voltmeter to see what the detector is "saying" at the point it connects to the Arduino, and/or feed the result from your detector circuit to an analog input.