Pop superstar Diana Ross graduated from lead singer of the most famous girl group in showbiz (The Supremes) to a solo act combining coy, feline sexuality with slick packaging. Despite obvious acting skills, however, movie stardom has eluded her thus far. She grew up in the Detroit projects, one of five children. By her late teens, she was singing in a quintet, The Primettes (distaff version of The Primes, a Motown group). In 1961, the group was down to a trio: Ross, Mary Wilson and Florence Ballard. They were renamed The Supremes and signed by Motown's star-maker, Berry Gordy Jr. Drilled in