Instructions
Install the original version of "Age of Empires III," if you haven't already. Insert the game's disc into your Mac OS X computer. Open the icon for the disc on your Mac desktop. Click "Next" to advance through the installation utility. Type the serial number on your game packaging into the installation utility. The original version of the game will install.
Install the "Age of Empires III" expansion pack. Both the original game and the expansion need to be installed on your machine in order to play the expansion pack. Insert the expansion's game disc into your Mac OS X computer and repeat the process that you went through when you installed the original version of the game. The expansion has its own unique serial number -- printed on the game's packaging -- that you must enter before installation can be completed.
Insert your "Age of Empires III" expansion pack game disc into your computer every time you want to play. You cannot run the game unless the disc is inserted into your computer. Open the icon for the game disc on your Mac desktop to open the game's launcher. Click "Play" to play the "Age of Empires III" expansion pack on your Mac OS X computer.