FYI: Desktop Effects are NOT entirely necessary for compositing:
Open the GNOME Configuration Editor; press Alt-F2 to open the Run Application dialog and type gconf-editor. Click Run. Navigate to Apps->metacity->general. Check the compositing_manager box, and Metacity will immediately restart with compositing!
docky will complain no more.
If you can't find an answer at Google, you must be typing in Braille.