  Since most high- and intermediate-mass protostars are at great distance and
form in clusters, high linear resolution observations are needed to investigate
their physical properties. To study the gas in the innermost region around the
protostars in the proto-cluster IRAS 05358+3543, we observed the source in
several transitions of methanol and other molecular species with the Plateau de
Bure Interferometer and the Submillimeter Array, reaching a linear resolution
of 1100 AU. We determine the kinetic temperature of the gas around the
protostars through an LVG and LTE analysis of their molecular emission; the
column densities of CH3OH, CH3CN and SO2 are also derived. Constrains on the
density of the gas are estimated for two of the protostellar cores. We find
that the dust condensations are in various evolutionary stages. The powerhouse
of the cluster, mm1a, harbours a hot core with T~220 (75<T<330) K. A
double-peaked profile is detected in several transitions toward mm1a, and we
found a velocity gradient along a linear structure which could be perpendicular
to one of the outflows from the vicinity of mm1a. Since the size of the
double-peaked emission is less than 1100 AU, we suggest that mm1a might host a
massive circumstellar disk. The other sources are in earlier stages of star
formation. The least active source, mm3, could be a starless massive core,
since it is cold (T<20 K), with a large reservoir of accreting material (M ~ 19
M_\odot), but no molecular emission peaks on it.
