Manpower needs help. The world's top staffing company shook investors on June 16 with an earnings warning. Rising costs from new information systems and from falling margins in French operations will cut second-quarter earnings by 39%. But some followers think Manpower's problems also stem from snagging too many big corporate accounts at thinner margins. Analyst Judith Scott of Robert W. Baird figures revenues will rise 16% this year, to $8.5 billion, but net will fall 29%, to $115 million.