This news from Havana: A U.S. flag was flown and the American anthem was played as Cuba welcomed eight young Americans to study medicine courtesy of the Cuban government. The six women and two men arrived in Havana late Tuesday and were welcomed yesterday. They are the first Americans to attend a free six-year program to become physicians, originally designed for impoverished students in Latin America. President Fidel Castro offered to extend the free medical training to include up to 500 Americans when he met last May with a delegation from the Congressional Black Caucus.