IDL stands for Indirect Diffuse Lighting - so, as has been stated, there is no specular component. As hborre says, it is equivalent to using a fill light in a classic 3 light setup (the others being a main and a rim or hair light), so a very simple setup would be a figure in a surrounding environment (like a sphere) plus a couple of normal lights. I've got a couple of demo's (not tutorials!) of a basic setup in my freestuff which could give you some useful info.

AO stands for Ambient Occlusion; it adds a soft shadowing effect to objects that are in close proximity as if the scene was evenly illuminated (ie. an overcast day). IDL includes an occlusion effect but it is superior in that it changes according to the scene lighting (or, that's my understanding at least). So IDL doesn't need AO on lights or materials - at best it will simply be ignored.

Hope that helps.

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