  In this paper, we estimate the gamma-ray and neutrino fluxes coming from dark
matter annihilation in a Milky Way framework provided by a recent N-BODY
HORIZON simulation. We first study the characteristics of the simulation and
highlight the mass distribution within the galactic halo. The general dark
matter density has a typical $r^{-3}$ power law for large radii, but the inner
behaviour is poorly constrained below the resolution of the simulation ($\sim
200$ pc). We identify clumps and subclumps and analyze their distribution, as
well as their internal structure. Inside the clumps, the power law is rather
universal, $r^{-2.5}$ in the outer part with again strong uncertainties for
smaller radii, especially for light clumps. We show a full-sky map of the
astrophysical contribution to the gamma-ray or neutrino fluxes in this N-body
framework. Using quite model independent and general assumptions for the high
energy physics part, we evaluate the possible absolute fluxes and show some
benchmark regions for the experiments GLAST, EGRET, and a km3 size extension of
ANTARES like the KM3NeT project. While individual clumps seem to be beyond
detection reach, the galactic center region is promising and GLAST could be
sensitive to the geometry and the structure of its dark matter distribution.
The detection by a km3 version of ANTARES is, however, more challenging due to
a higher energy threshold. We also point out that the lack of resolution leaves
the inner structure of subhalos poorly constrained. Using the same clump
spectrum and mass fraction, a clump luminosity boost of order ten can be
achieved with a steeper profile in the inner part of the sub-halos.
