To use IDL for indoor scenes, the simple answer is, place a light wherever you want there to be a light source.

For example, if you have a simple room with a couch, a pair of end tables and lamps, put a pair of point lights inside the lampshades, and set them to inverse square dropoff. If that is darker than you want, add an overhead light set to about 30% for openers. The purists will say you need all four walls, the ceiling and the floor in place, but the reality is, you can make the front wall transparent and it is still going to give a very usable (if not technically accurate) render. I've gotten very usable results out of the photobackdrop that comes in the Poser Pro 2012 primitive folder and one point light.

The whole idea behind IDL is to let the scene be lit as it would be in the real world, without using studio lights.

Typically, it takes much less light to get results using IDL than using the studio light setups. I do not know the technical reason, but this is the case. 

Outside, use BB's dome and one infinite light set to 10-30%.