On Monday's Late Show, David Letterman thanked the Montana authorities who helped unravel that alleged plot to kidnap his 16-month-old son. "Last week my family and I were involved in a little legal activity," he said, "and fortunately everything turned out fine, but I want to just take a second here to thank some people." Among the folks he singled out: two FBI agents, the local sheriff and "the great people of Choteau, Mont.," where he has a ranch. A handyman employed by Letterman was arrested Thursday and charged with solicitation, obstruction and theft. A hearing is scheduled for today.