Hi Hillary- what happens when you type MaterialEditor, anything at all? it should open the material panel, the same result as choosing Material Editor from the Panels menu. Any feedback at the command line? What version and service release of Rhino are you using? (Help> About Rhinoceros).
The commands you mention are from the RDK plug-in, can you check Options > Plug-ins for Rendrer Development Kit- is that enabled and loaded?