  Using numerical diagonalization techniques we analyze the finite
temperature/frequency conductance of a one dimensional model of interacting
spinless fermions. Depending on the interaction, the observed finite
temperature charge stiffness and low frequency conductance indicate a
fundamental difference between integrable and non-integrable cases. The
integrable systems behave as ideal conductors in the metallic regime and as
ideal insulators in the insulating one. The non-integrable systems are, as
expected, generic conductors in the metallic regime and activated ones in the
insulating regime.
