Well,from my experience,you can import 3d objects in PSCS4,(you’ll have to study in maya which one works best,obj,etc.),save it to a ps file and import it into AECS4…you’ll have then 3 layers: first one is the ps layer,asecond a null object to control the former and finally a camera. You Can rotate around the 3d object,is not a flat card,but integration is limited(does not react to AE lights,so no shadows,etc.)Lighting is done in PSCS4 and stays like that in AE (hard to explain,but believe me it’s the way it works).
I did a composition that had a 3d model of a rocket,and the environment was created with trapcode horizon…turned quite nice,the 3d universe created was acceptable…
Hope this helps…