  (Abridged) We present far-infrared (FIR) photometry at 150 micron and 205
micron of eight low-redshift starburst galaxies obtained with the ISO
Photometer. Five of the eight galaxies are detected in both wavebands and these
data are used, in conjunction with IRAS archival photometry, to model the dust
emission at lambda>40 micron. The FIR spectral energy distributions (SEDs) are
best fitted by a combination of two modified Planck functions, with T~40-55 K
(warm dust) and T~20-23 K (cool dust), and with a dust emissivity index
epsilon=2. The cool dust can be a major contributor to the FIR emission of
starburst galaxies, representing up to 60% of the total flux. This component is
heated not only by the general interstellar radiation field, but also by the
starburst itself. The cool dust mass is up to ~150 times larger than the warm
dust mass, bringing the gas-to-dust ratios of the starbursts in our sample
close to Milky Way values, once rescaled for the appropriate metallicity. The
ratio between the total dust FIR emission in the range 1-1000 micron and the
IRAS FIR emission in the range 40-120 micron is ~1.75, with small variations
from galaxy to galaxy. The FIR emission predicted by the dust reddening of the
UV-to-nearIR stellar emission is within a factor ~2 of the observed value in
individual galaxies and within 20% when averaged over a large sample. If our
sample of local starbursts is representative of high-redshift (z>1), UV-bright,
star-forming galaxies, these galaxies' FIR emission will be generally
undetected in sub-mm surveys, unless (1) their bolometric luminosity is
comparable to or larger than that of ultraluminous FIR galaxies and (2) their
FIR SED contains a cool dust component.
