There is a video-game quality to Nintendo's current streak: First, the fleeting prize, then the hidden trap door. On Sept. 5, the software company lifted its earnings estimate for the fiscal half ending Sept. 30, citing the weakening yen. The downside: Sales will be lower than expected, owing to the lackluster launch in Japan of the Virtual Boy 3-D game machine. Still, U.S. managers are smiling. The Killer Instinct game sold 150,000 copies in its first day--far more than 1994's hit, Donkey Kong Country.