The Digital Cinema Desktop (DCD) feature in Final Cut Pro HD 4.5 and Final Cut Express HD does not function in Main mode in Mac OS X 10.4 Tiger. This issue only occurs if you are using the feature in single-screen mode, which is referred to in documentation as "Digital Cinema Desktop Preview - Main." The other Digital Cinema Desktop Preview modes (which use two screens) work as expected.
This document will be updated as more information becomes available.