They're really not at the same level -- by that I mean, in a hierarchical sense of relationships, the 3 things are at different levels of the hierarchy.
Radiance transfer is just the idea of light getting from point A to point B. Global Illumination is just a term for the idea of trying to simulate all forms of radiance transfer (or at least enough of them to look good). Radiosity is simply one of many methods to achieve a Global Illumination solution of sorts.
The difference between RT and Precomputed RT is exactly what it sounds like. You've precomputed the radiance transfer for a scene using some arbitrary method and use that precomputed result to determine lighting behavior. In the case of trying to use it in a realtime situation, you'll use the precomputed result in a simplified form like a few spherical harmonics coefficients and just transform everything into the same basis.
