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 3×10^2 and 6×10^5 M[ scriptstyle sun ]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 mu m ( 1.8×10^12 Hz) to 25 keV ( 6.0×10^18 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.