The game works perfectly out of the box on my current machine (MacBook GMA 950, 10.6.7/CXG 10.10). I did have to use Eike Lang's registry edit hint as outlined in the Tips & Tricks section, though. There are some minor mouse control issues, but they can be solved thanks to this tip off of the GOG.com forums submitted by the_dro:
Go to C:\Program Files\GOG.com\XIII\system
Open the file : "XIII.ini", search and copy the following lines :
- "UseTripleBuffering=False"
- "UseVSync=False"
- "ReduceMouseLag=False"
(EDIT: This still works perfectly in CX11.)