WEST PALM BEACH, Fla. Apr 13, 2007 (AP)— Howard K. Stern, the former attorney and companion of Anna Nicole Smith, filed a slander lawsuit Friday against an attorney for Smith's estranged mother who has suggested Stern was involved in Smith's death. The lawsuit, filed in U.S. District Court in West Palm Beach, also accuses attorney John O'Quinn of invasion of privacy and seeks unspecified damages. A telephone message left by The Associated Press on Friday afternoon for O'Quinn was not immediately returned. O'Quinn is representing Smith's mother, Virgie Arthur, in a custody battle over Smith's baby. Smith died in February...