  We estimate the probability of detecting gamma-rays from the annihilation of
neutralino dark matter in dense, central regions of Milky Way substructure. We
characterize Galactic substructure statistically based on Monte Carlo
realizations of the formation of a Milky Way-like halo using a semi-analytic
method that has been calibrated against the results of high-resolution N-body
simulations. We find that it may be possible for the upcoming experiments GLAST
and VERITAS, working in concert, to detect gamma-rays from dark matter
substructure if the neutralino is relatively light ($\Mchi \lsim 100 \GeV$),
while for $\Mchi \gsim 500 \GeV$ such a detection would be unlikely. We perform
most of our calculations within the framework of the standard $\Lambda$CDM
cosmological model; however, we also investigate the robustness of our results
to various assumptions and find that the probability of detection is sensitive
to poorly-constrained input parameters, particularly those that characterize
the primordial power spectrum. Specifically, the best-fitting power spectrum of
the WMAP team, with a running spectral index, predicts roughly a factor of
fifty fewer detectable subhalos compared to the standard $\LCDM$ cosmological
model with scale-invariant power spectrum. We conclude that the lack of a
detected gamma-ray signal gives very little information about the
supersymmetric parameter space due to uncertainties associated with both the
properties of substructure and cosmological parameters.
