  We have studied the temperature dependence of the in-plane resistivity of
NbN/AlN multilayer samples with varying insulating layer thickness in magnetic
fields up to 7 Tesla parallel and perpendicular to the films. The upper
critical field shows a crossover from 2D to 3D behavior in parallel fields. The
irreversibility lines have the form (1-T/Tc)^alpha, where alpha varies from 4/3
to 2 with increasing anisotropy. The results are consistent with simultaneous
melting and decoupling transitions for low anisotropy sample, and with melting
of decoupled pancakes in the superconducting layers for higher anisotropy
samples.
