Well, if you haven't burned it out...
Green is probably GND, not voltage.
Black should go to a digital input.
Yellow should go to a digital output (likely thru a resistor, try a 1K, then drop to a 470 ohm, then to a 220 ohm).
The LED is likely IR - so unless you have a cheapo IR sensitive CCD camera somewhere (cheap webcams work)...you won't see anything.
Turn the yellow lead on (HIGH) with your digital write; monitor the pin the black lead is connected to. If you aren't getting any reading, try dropping the resistance down on the emmiter; don't go below 100 ohms (without knowing the specs of the emitter IR led, it is difficult to know what resistor to use).
You may have already burned it out; you probably couldn't see much anyway with even a webcam pointed at it, as the black plastic piece keeps things kinda directional.
I actually picked up a similar sensor yesterday, except mine has the leads going directly into the plastic piece (no PCB); and they are different colors - should be fun to figure out...