Variety reports that Zooey Deschanel will also star. Cumming will play Glitch, a scarecrow-like character, in the six-hour series, and Deschanel will play DG, a stand-in for Dorothy.
The miniseries is aiming to air in December 2007. Filming begins next month in Vancouver.
Cumming won a 1998 Tony for his portrayal of the Emcee in Sam Mendes' revival of Cabaret. He was recently seen in Martin Sherman's Bent on the West End, and on Broadway as Macheath in the Roundabout Theatre Company revival of The Threepenny Opera.
Other stage credits include Elle and Design for Living. In 1991 he won an Olivier for his performance in Accidental Death of an Anarchist. His films include "X2," the "Spy Kids" series and "Romy and Michele's High School Reunion."
Deschanel's film credits include "Almost Famous," "The Good Girl," "Elf," "The Hitchhiker's Guide to the Galaxy," Adam Rapp's film "Winter Passing," the new film "Bridge to Terabithia" and the upcoming "The Assassination of Jesse James by the Coward Robert Ford" and "Surf's Up."