I think the last post was back in November. Francesco, There is some very valuable information for you in this thread. Hope this helps. Most likely you will want to use the Accurate Intensities for your lighting settings. Check the Radiozity sample files to see what lighting settings are used for these projects.
Shadows are an option that needs to be selected in the rendering options.
All this is described in detail in your user's manual. If this does not provide you with the information that you need, you will need to be more detailed about what you are doing, and what the problem is.