  We discuss the question of the generation of topological defects
(dislocations) by quenched disorder in two dimensional periodic systems. In a
previous study [Phys. Rev. B {\bf 52} 1242 (1995)] we found that, contrarily to
$d=3$, unpaired dislocations appear in $d=2$ above a length scale $\xi_D$,
which we estimated. We extend this description to include effects of freezing
and pinning of dislocations at low temperature. The resulting $\xi_D$ at low
temperature is found to be {\it larger} than our previous estimate, which is
recovered above a characteristic temperature. The dependence of $\xi_D$ in the
bare core energy of dislocations is a stretched exponential. We stress that for
all temperatures below melting $\xi_D$ becomes arbitrarily large at weak
disorder compared to the translational order length $R_a \gg a$. Thus there is
a wide region of length scales, temperature and disorder where Bragg glass like
behavior should be observable.
