Americans Dan Jansen and Eric Flaim were winners here Saturday in the first day of a World Cup speed skating event. Jansen, of West Allis, Wis., won the 500 meters in 36.91 seconds, beating Olympic gold medalist Jens-Uwe Mey of East Germany. Flaim, a silver medalist at the 1988 Olympics at 1,500 meters, won that race Saturday in 1:55.87.