David Letterman is headed to ABC — albeit for one night only. According to the The New York Times, the Late Show host has agreed to a sit-down interview with Ted Koppel to air the week of July 8 on ABC's new profile-oriented spinoff, Nightline: Up Close. Koppel asked Letterman for the interview back in March, after the whole "Will Dave replace Ted on ABC?" brouhaha was resolved — with Letterman staying put on CBS. "Dave is no show-business weasel," says Late Show exec producer Rob Burnett. "He promised Ted, and he's going to do it."