Now that Sundance has been thoroughly assimilated by Hollywood, the film festival is being challenged by not one but two counter-festivals. Jon Fitzgerald and Peter Baxter actually began their alternative programming in 1993, when they started Slamdance as a showcase for filmmakers whose work was excluded from Robert Redford’s Amerindie gala. The duo will show “Selections From Slamdance” and discuss their approach to film and festivals at 8 p.m. tonight and tomorrow at the Hirshhorn Museum & Sculpture Garden’s Ring Auditorium, 7th & Independence Ave. SW. FREE. (202) 357-2700. (MJ)