GREY'S ANATOMY - "The Time Warp" - In his new role as Chief, Derek restores the hospital lecture series, and Richard, Bailey and Callie present to the group pivotal surgical cases from their pasts - Bailey reflects on her first days as a shy resident, Callie looks back on a polio case, and Richard recalls a case in which he and Ellis worked on a patient diagnosed with GRID, a virus later called AIDS -- on "Grey's Anatomy," THURSDAY, FEBRUARY 18 (9:00-10:01 p.m., ET) on the ABC Television Network. (ABC/RON TOM) JAMES PICKENS JR.