Now, I've hit a brick wall, in several ways.
First and foremost, the scene I'll be doing will have a large room with a hatch at the top, which opens and lets sunlight inside. This means the camera will have to be inside the volumetric container. But the second the camera enters the volumetric container, the volumetric effect vanishes! The animation test I've linked below shows this quite clearly. Why's it doing this, and how do I get it to work?
Secondly is a matter of atmosphere. How do I achieve the sense of realistic volumetric light, of dust flying through the air getting illuminated by the sun rays and adding to the volumetric effect? Is this best done with a shader, or with a particle system? Give me some pointers, or more in-depth tips if you have the time!