All Spore DVDs include Mac installers alongside the Windows exe installers. For the base game and GA, they install the game inside of an emulator called Transgaming Cider, which emulates a Windows system and file structure. Therefore, Spore installs to the same directories inside of the emulator, as it would on a Windows system.
As C&C is only a single file (BoosterPack01.package), the C&C installer just has to add this file to the game directory. The DVD includes both Windows exe and Mac installers to accomplish this. The modern Origin versions however, use a different installer that is only compatible with Windows.
The parts pack itself is the same one file for all versions of Spore, for both Windows and Mac.
As the Mac version of the game runs in a Windows emulator, the game directories mirror the Windows version of the game exactly. Therefore, the C&C file can be placed exactly in the same spot that it would be on a Windows system. Depending on how both the game and C&C were installed, this could be one of three locations - that is why i provided all three.
I know for certain that installing from DVD works fine on a Mac (got a friend to test it, and also MaxisBazajaytee confirmed this on that same thread i linked), and I also know from another friend that manually placing the BoosterPack package file in the Spore\Data folder works fine - which it is always should, the game loads it's own data from this folder so it will always load package files placed here.
I haven't had anyone test the other two paths yet, but I suspect now that they would only work if C&C had been previously installed. The reasoning for this is, the game seemingly uses the registry to determine where to load package files from (transgaming cider emulator does also emulate the windows registry as its used by Spore). If C&C has never been installed, the registry key will not exist and therefore the game will not know to look in the other two folders. I have not yet found a way to edit the emulated registry on the mac version.
