Upper Deck will begin airing ads for its Avatar: The Last Airbender Trading Card Game  (see 'World of Warcraft is Upper Deck's Major Initiative') in five markets on Monday, April 17th.  The markets are New York, Los Angeles, Chicago, Philadelphia, and Boston.  The ads, which will appear on Nickelodeon (home of the Avatar animated series) and Cartoon Network, will continue for three weeks.