I'm trying to figure out this stuff too, Brian, as I go along. So you are not alone. I think I figured it out. Replica doesn't work with grouped objects when it comes to populating a terrain because only the group name gets replicated a zillion times and not the actual objects within the group. A Poser figure imported using Transposer counts as one object rather than a group of objects. So I was able to replicate one along a terrain. Importing an Amapi figure (so far) using AmapiImporter results in a grouped figure which won't do. This picture has lots of the default Poser 5 dude. Make sure you have 4GB RAM with just this many instead of only 1GB RAM before hitting that render button.

www.youtube.com/user/ShawnDriscollCG