FEEL like putting your vivid imagination to good use? RTHK Radio 3's Kidshour has come up with a perfect idea that may kick-start the careers of many a budding fiction writer. The programme (broadcast Monday to Friday between 4 pm and 5 pm) will offer a short story competition under which participants will write a 500-word story with the beginning line ''A magic place . . .'' Participants will receive complementary prizes from Futurekids, a computer-learning centre. Competitors will be divided into two categories - 10 years and under and 11-16 years. The first/overall winner (from either category) will take home a Compaq home computer worth $10,999. The first prize winner (in both categories) will receive 12 computer lessons and a $800 cash voucher.