Bob Costas, who is for my money the best interviewer on television, is sitting in for Larry King this week. Last night, he spent the hour with Conan O'Brien. Tonight, he and his guests discuss the BTK Killer — and every time I see that phrase, I think it's some new sandwich at Burger King. Mr. Costas has also resumed his Costas Now program on HBO which mostly discusses sports in a manner that will even interest people who are not much interested in sports.