You don't need to use wacros or anything. As I said, on Poser's ground plane, the shadow_cast_only is allreadt checked so you can simply use the ground plane to get the shadows. Remember that at least one of your lights must be set to cast shadows (raytraced or shadow mapped that doesn't matter) and that Shadows must be turned on in the render settings. The default, rather crappy render setting in P6 does NOT have shadows switched on IIRC...

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.