  We study numerically the effects of temperature on moving vortex lattices
interacting with periodic pinning arrays. For low temperatures the vortex
lattice flows in channels, forming a hexatic structure with long range
transverse and longitudinal ordering. At higher temperatures, a transition to a
smectic state occurs where vortices wander between channels and longitudinal
order is lost while transverse order remains. At the highest temperatures the
vortex lattice melts into an isotropic liquid.
