  Spectral fits to X-ray data from both NGC 253 and M 82 provide ambiguous
results. The so-called ``best fit'' results depend on the instrument with which
the data were obtained and obviously on the choice of spectral model
composition. We show that different spectral models can be fit equally well to
BeppoSAX data of both galaxies. Metallicities are unreliable in general, with a
strong dependence on the choice of model. Preference to one particular spectral
model can only be given by combining spectroscopic and imaging X-ray data from
all available satellites (ROSAT, ASCA, and BeppoSAX). Based on spectra of NGC
253, we demonstrate that a model consisting of two or more thermal plasma
components plus a hard power law continuum and Fe K alpha line emission can
explain all observations. These model components represent the integral
spectrum of thermal gas and compact sources in starburst galaxies that are most
likely supernova remnants and X-ray binaries. The same model can fit the X-ray
data of M 82, but there the evidence, from ROSAT imaging, of the existence of
compact sources which might represent high-mass X-ray binaries is weaker. This
implies that its hard X-ray emission, which is extended in ROSAT images, might
- if truly diffuse - be dominated by a very hot (several keV energy) thermal
gas component.
