NOTE:
The Digital Rights Management (DRM) software in this program might prevent it from running in CrossOver. If you are in a legal jurisdiction which allows removal of such software, you may have luck running this program. Unfortunately, CodeWeavers, because they are subject to the Digital Millennium Copyright Act, will be unable to support you.I installed DS on Mac with Leopard in a WinXP bottle with the newer versions of Crossover Games (8.1.4), but found that when I started the first game, a warning came up that the resolution was unsupported and that problems would result. The video was horrible and game unstable.
To fix this, run Dungeon Siege Video Configuration, in the Troubleshooting folder in the installed Dungeon Siege folder and set the resolution to something else, like 1024 x 768 32.
Next, in the Bottle manager, in the Control Panel, run winecfg and in the Graphics tab select the checkbox to have it emulate a virtual desktop with the same resolution.
Once you do this, you can start the game again and the major video problems should resolve.