We study thin, symmetric AB-copolymer films between neutral walls using the bond fluctuation model. Near the surface, the monomer distribution with respect to the chains' center of mass is nonisotropic: The chains flatten on the surface. The resulting A- and B-lamellae have interfaces practically perpendicular to the walls, as also observed in recent experiments. Our simulations indicate the onset of long-range surface ordering before the bulk orders. The strongest effects take place between the spinodal and the order-disorder transition point of the diblock copolymer melt.