Elvis Costello, Kim Cattrell, Eddie Izzard, Mitch Hedberg

Will Ferrell joins fellow ""Old School"" star Vince Vaughn as a guest host on Letterman. In his monolouge, Will does his famous George W. Bush impression and serenades the absent host with his version of Kenny Rogers' ""Lady."" Later on, the up and coming rock band The American Hi-Fi performs their hit ""The Art of Losing.""