I had dropped this forum from my list after somebody complained that they were told
to ask somewhere else, and I sure hope you ain't asking in the wrong place, ladylindael.
I don't get in here more than twice a week (be back monday barring unforeseen stuff)
but basically ya do yer render with depth cue enabled, export yer render as tiff file,
open that in cs3, then select channels, select mask (alpha), then go back to the
layer and apply filter thru mask.

the rest of 'em know how to do this, hence they can add more info, if needed.