Ratings for NBC's Today show shot up Wednesday as Meredith Vieira made her much heralded debut, replacing Katie Couric. Today didn't see the same sort of ratings rocket that Couric's debut on the CBS Evening News did last week, but it was certainly substantial. Wednesday's broadcast attracted 6.9 million viewers, up from an average 5.8 million last week. (ABC's Good Morning America counted 4.6 million viewers; CBS's The Early Show, 2.7 million. Today was also helped by Matt Lauer's exclusive interview with Debra Lafave, the former teacher who admitted having had sex with a 14-year-old student. Meanwhile, Rosie O'Donnell's debut on The View, replacing Vieira, gave the show its biggest seasonal start in its 10-year history.