It's not easy being rich. There are expensive cars to buy, blobs of caviar to eat, old friends to ignore. So how does the aspiring millionaire learn how to live up to his Diamond Jim destiny? In school, of course -- specifically, the University of Denver, which last year made "Who Wants to Be a Millionaire" one of its seventy freshmen seminars. Professor Robert Mills offered students their choice of several millionaire lifestyles, then reported on how they would live them out. The one-credit class was one of seventy freshman seminars intended to keep students interested in school. Now, about that financial aid.