  We estimate the condensation temperature for microcavity polaritons, allowing
for their internal structure. We consider polaritons formed from localised
excitons in a planar microcavity, using a generalised Dicke model. At low
densities, we find a condensation temperature T_c \propto \rho, as expected for
a gas of structureless polaritons. However, as T_c becomes of the order of the
Rabi splitting, the structure of the polaritons becomes relevant, and the
condensation temperature is that of a B.C.S.-like mean field theory. We also
calculate the excitation spectrum, which is related to observable quantities
such as the luminescence and absorption spectra.
