I *may* be mistaken, but I do think that "newer" (as of the past so many years) versions of the CD (ie, is your CD on patch 1.06?) only contain the OSX installer. The original CDs had the classic Mac OS environment installers on it.
I may be remembering incorrectly though... I'd recommend posting this in the Open Tech Support forum instead, and I'd recommend checking out www.blizzard.com/support to browse the FAQ's on this. I do know there are certain installers Mac users need to download, but I remember them all being for OSX.