After spending two weeks drawing ratings no better than those that Conan O'Brien averaged when he hosted NBC's Tonight show, Jay Leno moved up a bit last week. True, his ratings increased just a tenth of a point above O'Brien's, but Leno's certainly not complaining. His tiny ratings climb came at the expense of David Letterman, whose numbers for the Late Show on CBS slipped a tenth of a ratings point. Meanwhile, ABC's Nightline seemed to be benefiting from the talk-show wars, coming in a strong second among all viewers, viewers 25-54 and viewers 18-49.