  We derive an approximate theory for Heisenberg spin ladders with two legs by
mapping the spin dynamics onto the problem of hard-core `bond-Bosons'. The
parameters of the Bosonic Hamiltonian are obtained by matching anomalous
Green's functions to Lanczos results and we find evidence for a strong
renormalization due to quantum fluctuations. Various dynamical spin correlation
functions are calculated and found to be in good agreement with Lanczos
results. We then enlarge the effective Hamiltonian to describe the coupling of
the bond-Bosons to a single hole injected into the system and treat the
hole-dynamics within the `rainbow-diagram' approximation by Schmidt-Rink et.
al. Theoretical predictions for the single hole spectral function are obtained
and found to be in good agreement with Lanczos results.
