It seems that there was a Mac version that ran native on the Power PC versions of the Mac. This is no longer supported and I have an intel based Mac anyway.
It seems that the game will/should run under an emulator. The obvious candidates are Parallels, VMware or even Virtual Box. This means buying a copy of windows which is getting hard since they're about to churn the base again from Vista to W7.

I got this from the Bioware Mac User forum. I might come back and document the URLs for the key threads and old resources.
Where does one get a copy of Windows XP, that'll work with Windows Update?
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Dave