The game from Macintoshgarden installs fine in OSX 10.5.
To run the game, the app looks for the physical CD-2. There are a lot of no-CD patches listed in a thread at Macintoshgarden, maybe that will help.
I get stuck here and do not know where to fix according to the requester. The readme points to .ini in the user/ducuments/dungeonsiege folder, but that does not help me.
"DrawSprocket cannot switch to the requested resolution (800x600, 16bit, 1 buffer).
Make sure your computer meets the display requirements specified in the Read Me file."
Maybe QEMU emulating a G3 Mac will run the game?