I stumbled on this article that was 100% spot on. Credit to the author, I had nothing to do with it.
Once you get the hang of how to use the arduino, simply flash the code located in KegArduino and it should be good to read the pulses from the flow meter (once we hook it up).
The arduino will get its power from the raspberry pi USB connection, so you won't need to have an AC->DC adapter on there.