Dockyard was a program that allowed you to have multiple docks and switch between them via the menu bar, a Dashboard widget, or a standalone application. Unfortunately, incompatibility with Spaces and a large codebase led to its retirement. For a program that provides similar features, take a look at Dock Spaces from NSCoding.
Custom menu extras have been prohibited on Mac OS X for several versions, so the Dockyard menu extra will not run without a separate enabling plug-in. I am not sure if any such plug-ins are available for Mac OS X v10.6 (Snow Leopard).
for Xcode 2.1