Lipflip.org has released an installer package for the dict.cc version of a German-English dictionary. The installer, compatible only with Leopard, installs the dictionary into Leopardis Dictionary.app.
After installation, the dictionary is enabled in the preferences of the Dictionary.app. In addition to normal use in the Dictionary application, users can right-click the unknown word in any Cocoa App and select "Dictionary". Alternatively one can select CTRL+CMD+D and move the mouse cursor over the words a sentence for translation.
The installer is licensed under the GPL and the actual dictionary has its own license. The German-English dictionary for Leopard is free.