  In this contribution we evaluate the minimal cluster mass for which the
effects of an incomplete sampling of the Initial Mass Function (IMF) cannot be
neglected. This minimal cluster mass corresponds to the situation in which the
integrated luminosity of the cluster modeled equals the luminosity of the most
luminous individual star included in the model, and it takes values between
3x10^2 and 6x10^5 Mo depending on the age and the observed band. We show
different examples for young (t < 10 Myr) and old (t up to 10 Gyr) stellar
populations. We also make here a first release of the spectral energy
distribution (SED) from 160 mic. (1.8x10^12 Hz) to 25 keV (6.0x10^18 Hz) for
star-forming regions with ages between 0.1 and 10 Myr, and metallicities
between Z=0.001 and Z=0.040. The SEDs are available at our WWW server and
include the corresponding quantities for the evaluation of sampling effects.
These SEDs can be directly used to obtain colors (including the X-rays ones),
as input of photoionization codes, or for chi^2 fitting with observed data
taking into account the intrinsic uncertainty of the models due to the IMF
sampling.
