Louise McBain has been building a $600 million publishing empire af arts magazines. Now she’s restructuring. “In five years, MacBain bought Art + Auction, Modern Painters and Museums Magazines and Gallery Guides, which publish guides for eight or more cities each. She added a data service, Art Sales Index, and a French publisher, Somogy. She launched a Web site, Artinfo.com, in 2005, and Truman will help start a new magazine, Culture & Travel, in September.”