NEW YORK/GENEVA (Reuters) - Advanced talks have bogged down on a multibillion-dollar deal between Switzerland and the United States over Swiss banks helping Americans to shield their money from the U.S. taxman, two sources briefed on the matter said Tuesday. (http://feeds.feedburner.com/~ff/reuters/topNews?d=yIl2AUoC8zA) (http://feeds.feedburner.com/~ff/reuters/topNews?i=M5cKQy5E8qo:M63PIa2Mvzg:V_sGLiPBpWU) (http://feeds.feedburner.com/~ff/reuters/topNews?i=M5cKQy5E8qo:M63PIa2Mvzg:-BTjWOF_DHI) (http://feeds.feedburner.com/~r/reuters/topNews/~4/M5cKQy5E8qo)