  Effects of disorder on the two competing phases, i.e., the ferromagnetic
metal and the commensurate charge/lattice ordered insulator, are studied by
Monte Carlo simulation. The disorder suppresses the charge/lattice ordering
more strongly than the ferromagnetic order, driving the commensurate insulator
to the ferromagnetic metal near the phase boundary in the pure case. Above the
ferromagnetic transition temperature, on the contrary, the disorder makes the
system more insulating, which might cause an enhanced colossal
magnetoresistance as observed in the half-doped or Cr-substituted manganites.
No indication of the percolation or the cluster formation is found, and there
remain the charge/lattice fluctuations instead which are enhanced toward the
transition temperature.
