One day I realized that my entire back seat was filled with relatives who wondered why I wasn't paying more attention to their part of the family story. . . . Sooner or later they all come up to the front seat and whisper stories in my ear.   Growing up in the 1950s in suburban Minneapolis, Diane Wilson had a family like everybody else's. Her Swedish American father was a salesman at Sears and her mother drove her brothers to baseball practice and went to parent-teacher conferences.   But in her thirties, Diane began to wonder why her mother didn't speak of her past. So she traveled to South Dakota and Nebraska, searching out records of her relatives through six generations, hungering to know their stories. She began to write a haunting account of the lives of her Dakota Indian family, based on research, to recreate their oral history that was lost, or repressed, or simply set aside as gritty issues of survival demanded attention.   Spirit Car is an exquisite counterpoint of memoir and carefully researched fiction, a remarkable narrative that ties modern Minnesotans to the trauma of the Dakota War. Wilson found her family's love and humor--and she discovered just how deeply our identities are shaped by the forces of history.