New York--Ziff Davis Media Inc. on Tuesday named Robert Callahan, formerly president of the ABC Broadcast Group, as chairman and president-CEO of the struggling technology publisher. Callahan starts Oct. 1. Jim Dunning was fired earlier this summer by Willis Stein & Partners, the venture capital firm that owns Ziff Davis, as ad pages and ad revenue plummeted at several of Ziff's trade titles. During his ABC tenure, Callahan oversaw the entire network, including ABC News and ABC Sports. Prior to joining ABC, Callahan spent 10 years at Fairchild Publications in several senior executive positions.