Acclaimed conductor Hans Graf makes his final appearance as music director of the Houston Symphony during today's A Graf Farewell concert. Mahler's massive and extremely dramatic Symphony No. 2, Resurrection is on the program. Beginning with a death march and concluding a hymn, Resurrection has the most uplifting ending of all of Mahler's symphonies, according to the departing Graf. ''There is a spiritual element in it that is hard to beat,'' he says. Guest artists Erin Wall (soprano), Bernarda Fink (mezzo-soprano) perform along with the Houston Symphony Chorus under the direction of Charles Hausmann.