I’m trying to adapt Colin Litster’s classic nebula tutorial (PDF) to Blender 2.5 alpha 2 and, so far, the gaseous effect isn’t happening. I suspect that maybe the texture isn’t being applied to the mesh properly: the overall glow and alpha parts look right, but it lacks any wispy, nebulous appearance.
Okay, with the render emitter option off, it gets better:
Here’s the basic idea. It needs a fair amount of work to look really good, but the concept is there: