  We derive new constraints on the mass of the Milky Way's dark matter halo,
based on a set of halo stars from SDSS as kinematic tracers. Our sample
comprises 2401 rigorously selected Blue Horizontal-Branch (BHB) halo stars
drawn from SDSS DR-6. To interpret these distributions, we compare them to
matched mock observations drawn from two different cosmological galaxy
formation simulations designed to resemble the Milky Way, which we presume to
have an appropriate orbital distribution of halo stars. We then determine which
value of $\rm V_{cir}(r)$ brings the observed distribution into agreement with
the corresponding distributions from the simulations. This procedure results in
an estimate of the Milky Way's circular velocity curve to $\sim 60$ kpc, which
is found to be slightly falling from the adopted value of $\rm 220 km s^{-1}$
at the Sun's location, and implies M$(<60 \rm kpc) = 4.0\pm 0.7\times
10^{11}$M$_\odot$. The radial dependence of $\rm V_{cir}(r)$, derived in
statistically independent bins, is found to be consistent with the expectations
from an NFW dark matter halo with the established stellar mass components at
its center. If we assume an NFW halo profile of characteristic concentration
holds, we can use the observations to estimate the virial mass of the Milky
Way's dark matter halo, M$_{\rm vir}=1.0^{+0.3}_{-0.2} \times
10^{12}$M$_\odot$, which is lower than many previous estimates. This estimate
implies that nearly 40% of the baryons within the virial radius of the Milky
Way's dark matter halo reside in the stellar components of our Galaxy. A value
for M$_{\rm vir}$ of only $\sim 1\times10^{12}$M$_\odot$ also (re-)opens the
question of whether all of the Milky Way's satellite galaxies are on bound
orbits.
