To compile DGD on a Mac, you'll need Symantec C 7.0.4 or newer.

De-binhex dgd.proj.hqx and dgd.rsrc.hqx.  Move the project file up two
folders (into the src folder), and double-click it to start the Project
Manager.  If you have any trouble with the compiler selecting the wrong
source files, remove all the non-Mac folders from the src:host folder.

If you want to compile DGD with CodeWarrior, you'll have to make your
own project file.  Make sure that the size of an integer is 4 bytes,
and that the symbol MACOS is #defined.  Also, compile for 68000 rather
than PowerPC, and turn off the "high level event aware" size flag.