MoMA is in full preparation mode for its second blockbuster of the season. First, there was the universally praised, monumental "Richard Serra Sculpture: Forty Years," and this weekend brings another post-Minimalist sculptor, Martin Puryear. Five of the 45 works slated for the exhibition are already on display in the museum's airy second-floor atrium, the eerie, Surrealist Ladder for Booker T. Washington, among them. Kids were free to explore Serra's winding arcs, but it's safe to say that this work, no matter how enticing, is decidedly hands off. —Rachel Wolff