Hi,
There are two locations on your Mac in which the game will put files. The first is in Applications, in a folder called 'The Sims 3' - this is where the actual game files are installed. The second location is in Documents, where there is a folder called 'Electronic Arts' and within that a folder called 'The Sims 3' - this is where your saved games etc are kept.
When you are installing an expansion pack, when the installer asks you to select a volume, make sure you choose the Applications portion of your hard drive.
Caspin
