NBC, which had much to cheer about last week as more than 18 million viewers tuned in for the debut of the Jay Leno Show , must have been stunned after getting word today that ratings for the show had disintegrated after just a week. Monday's episode attracted just 5.67 million viewers, about what he was drawing when Leno hosted the Tonight show. Even more worrying, perhaps, was the sickly performance of a two-hour season debut of Heroes, which preceded the Leno show. It drew a fourth-place 6.02 million viewers. A year ago, the season premiere of Heroes attracted 10.09 million viewers. ABC's Dancing With The Stars was the big winner Monday night as it kicked off the season with a two-hour episode that landed 17.53 million viewers. Fox's House was close behind with 16.50 million viewers.