  We study the nanoscale phase coexistence of ferromagnetic metallic (FMM) and
antiferromagnetic insulating (AFI) regions by including the effect of AF
superexchange and weak disorder in the double exchange model. We use a new
Monte Carlo technique, mapping on the disordered spin-fermion problem to an
effective short range spin model, with self-consistently computed exchange
constants. We recover `cluster coexistence' as seen earlier in exact simulation
of small systems. The much larger sizes, $\sim 32 \times 32$, accessible with
our technique, allows us to study the cluster distribution for varying electron
density, disorder, and temperature. We track the magnetic structure, obtain the
density of states, with its `pseudogap' features, and, for the first time,
provide a fully microscopic estimate of the resistivity in a phase coexistence
regime, comparing it with the `percolation' scenario.
