Seeing objects through other objects

Hi All
We need a solution -
as we have multiple objects, mapped with .png having transparencies in various parts of the object , if we are walking along the level where the objects are placed we are able to see the objects behind overlaping the objects facing the camera.

we have tried exporting objects with -rendering options - two sided from dts exporter.
we use maya 6.5 .

Plz provide with a solution.

Thanks.