Attached Link: http://www.blender.org/modules/documentation/htmlI/c8778.html

If I understand your question correctly MrDB, you can use spotlights to cast shadows at the same time as you are using Radiosity, or GI. Maybe this is the only way to get the effect you describe. In case you haven't seen it, there is a four-page section concerning radiosity in the Blender online manual/user's guide that might answer a few of your questions. Too bad they haven't written the ray-tracing section yet.