  We present an analysis, using quenched configurations at $6/g^2=$5.7, 5.85,
6.0, and 6.3 of the matrix element $\MP\equiv\langle \bar P_{hl}|\bar h
\gamma_\mu (1-\gamma_5)l \bar h \gamma_\mu(1-\gamma_5)l|P_{hl}\rangle$ for
heavy-light pseudoscalar mesons. The results are extrapolated to the physical
$B$ meson states, $\Bd$ and $\Bs$. We directly compute the ratio $\MS/\MB$, and
obtain the preliminary result $\MS/\MB=1.54(13)(32)$. A precise value of this
SU(3) breaking ratio is important for determining $V_{td}$ once the mixing
parameter $x_s$ for $\Bs-\bar\Bs$ is measured experimentally. We also determine
values for the corresponding B parameters, $B_{bs}(2 \rm{GeV})=B_{bd}(2
\rm{GeV})=1.02(13)$, which we cannot distinguish in the present analysis.
