[koenig3456]

Since the wheels are mounted on opposite sides of the robot, they need to be operated opposite from each other. For example: To drive straight you would use:
SetMotor ( L_MOTOR , 255 ) ;
SetMotor ( R_MOTOR , 0 ) ;

Try swapping the SetMotor ( R_MOTOR , 255 ) ; and SetMotor ( R_MOTOR , 0 ) ; calls.