(Hillsboro, OR)  --  Hillsboro police are investigating the death of a pedestrian on the Tualatin Valley Highway.  Authorities say the 51-year-old man was crossing the highway early yesterday morning near Southwest Cornelius Pass Road when he was struck by a sedan.  The "Portland Tribune" reports the 29-year-old driver, Beatriz Rivera of Issaquah, Washington, was arrested on an unrelated misdemeanor warrant for violation of probation.  The pedestrian's name hasn't been released.