Was she talking about marriage between a man and another man or a woman and another woman, which, of course, Newt Gingrich excludes from the definition of marriage? No, she was talking about a marriage between a man (Newt) and a woman (her) in which the woman does not have the man all to herself but will share him with another woman (Callista, who accepted the concept of sharing):
ADDED: If the embedded video doesn't work for you, go here.
UPDATE: Just watched the "Frontline" interview. I thought it was nothing (aside from the strange allegations against Marianne having to do with meeting with an arms dealer and asking for $10 million). Basically, it's the same story we always knew. He had an affair, and then they got divorced. I don't really understand her motivation to go on camera to say that. She seems like a very grim and sad woman.