For a Virtex-4 FPGA design, after importing ISE design tools placement or an Implementation result in the PlanAhead software, the DCM placement is not shown in the Device View or the Object Properties View.
This problem is caused by the DCM Auto-calibration logic insertion for Virtex-4 devices described in (Xilinx Answer 21435).
PlanAhead design tools placement is only shown if it can be correlated back to a netlist instance. The DCM Auto-calibration logic insertion changes the DCM name during MAP, so PlanAhead tools are not able to match the DCM placement to the DCM instance in the netlist.
To overcome this problem, either disable the DCM Auto-calibration logic insertion (Xilinx Answer 21435) or manually place the DCM instance and the Auto-calibration logic in the PlanAhead tool. You can find their placement by opening the routed NCD in FPGA Editor.