Mullally is remembered by theatregoers as Rosemary Pilkington in the 1995 revival of How To Succeed in Business Without Really Trying opposite Matthew Broderick. Her other stage creds include Marty in the 1994 revival of Grease. Also scheduled to guest host this week are actor Vince Vaughn ("Swingers"), singer Elvis Costello and former "Saturday Night Live" comedian Will Ferrell. Prior to the last week's previously scheduled hiatus, actor Bruce Willis and talk show host Regis Philbin headed up the late-night show. No host has been announced yet for this Friday's show. Current Ma Rainey's Black Bottom star Whoopi Goldberg served as host March 10.

Costello, who was scheduled to perform as musical guest March 12, will take on both hosting and musical guest duties for the evening. His guests include the upcoming star of the Roundabout Theatre Company's revival of A Day in the Death of Joe Egg Eddie Izzard and "Sex and the City" actress Kim Cattrall.

For more information on "The Late Show With Dave Letterman," visit www.cbs.com.