do I have to precalculate all of my cubemapped surfaces or are they real time
Both are possible...
Drive up to it in my space ship... Will I see my ships reflection?
If you render a runtime cubemap, why not. Do note that DX7 (non-shader) reflections are polygon based, meaning that they will look quite horrible (warpy) if you don't have enough dense mesh.
Cubemaps explained (.PDF)
developer.nvidia.com/attach/6666