Charodei

Having run into difficulty getting BGT to install on my Mac, I decided to take a different approach: install the Windows version, then copy the data files over to the Mac. This worked quite well, with only a couple of surprises.

My procedure:
On a Mac, install ToB and the official patch. I did a full install, but that may not be necessary.
On a Windows machine, do a full install of BG/TotSC/BG2/ToB and official patches.
Install BGT and any other desired patches/mods. Don't use any that modify the .exe, since you won't be running it.
Copy the entire BGT folder over to the Mac; you may want to go out to lunch while you wait. (If the only available PC is a laptop with a wireless connection, go out to a football game instead.)
On the Mac, copy Baldur's Gate II (app), BGConfig, and Baldur.ini into the BGT folder.
Create a folder named 'temp' if it doesn't exist yet. (This fixes a bug in the ToB patch.)
Finally, we have to modify Chitin.key because the path separators are different; I recommend using a hex editor for this. Replace every occurrence of 'data\' with 'data:' and 'movies\' with 'movies:'. Case is not important.

I haven't done any in-depth testing beyond starting new games in each of the three parts, but it appears to be working properly. The only problem is that BG1 characters are still generated at level 7, but a save-game editor can fix that.