Experts from score of universities nationwide are preparing recommendations for government as Justice Dept and 19 states prepare for penalty phase of Microsoft antitrust trial; The New York Times interviews five other academic authorities or former government officials who maintain direct professional interest in case but are not attached to either Microsoft or government; they discuss remedy they would choose; they are Nicholas Economides , economics professor, William J Baer, former director of Federal Trade Commission, Robert Litan, economic studies director, Robert E Hall, economist, and Steven Salop, professor of economics and law; photos