Sorry for the delayed answer. "Mega 2560" only refers to the processor on the board, if you compare the two boards you'll notice that they have the same processor.
However, you are correct that your standard Mega board is missing a few components to use the ADK protocol.
The ADK board: http://arduino.cc/en/Main/ArduinoBoardADK
(presumably) your board: http://arduino.cc/en/Main/arduinoBoardMega2560
There are a number of different ADK (and ADB) shields out there, however I'm very reluctant in recommending any of them since I haven't tested their compatibility myself. A search for "Arduino ADK Shield" should yield a couple of choices (if they work with the standard Arduino ADK libraries then they should
work for the examples in the book)