The connection of distributed energy resources (i.e., distributed generation and energy storage) and some special loads (e.g., electrical vehicle) raises new challenges in distribution system analysis. Intermittent and non-dispatchable generation units, time-dependent or asymmetrical loads require capabilities that until very recently were not available in distribution software packages; for instance, capabilities for probabilistic and time mode simulations. This paper presents the work made by the authors to adapt OpenDSS, a freely available distribution simulator, in order to perform these types of studies taking into account that the model of an actual distribution system is usually very large and complex. A goal of the paper is to present the usage of OpenDSS as either a stand-alone tool or as a COM DLL driven from MATLAB. Several applications have been developed to obtain yearly curve shapes aimed at representing time-varying loads and renewable energy sources (sun, wind) and to run OpenDSS in a distributed computing environment (e.g., multicore installation).