GREY'S ANATOMY - "Desire" - As the interns of Seattle Grace cram for their upcoming exam, the attendings vie for the Chief's position by tending to the chairman of the hospital board after he's admitted as a patient. Meanwhile, Burke struggles to involve Cristina in the wedding planning, things heat up between Addison and Alex, and Derek questions his relationship with Meredith, on "Grey's Anatomy," THURSDAY, APRIL 26 (9:00-10:01 p.m., ET) on the ABC Television Network. (ABC/GALE ADLER) MARY-MARGARET HUMES, ROWENA KING