Syndicated radio host Don Imus, who suffered serious multiple injuries after being thrown from a horse in New Mexico on Father's Day, returned to the airwaves yesterday -- with oxygen tubes attached to his nostrils. The still-recovering I-Man also had trouble moving his left side. Still, he remained in rare form. He slammed those who sent him sympathy cards, especially Hillary Rodham Clinton and Al Gore, who have both been Imus targets for years. After reading Gore's message, Imus, 59, called the Presidential aspirant a "moron," and then went on to call Clinton's card "pathetic . . . This woman wanted me dead!" (He suggested that he might set fire to Hillary's card, but then again, the oxygen tank to which he was attached might explode.) Oddly, Imus had kind words for his arch rival Howard Stern. "He said he wished I'd die," said Imus. "That's why I like Howard -- he's consistent."