I don't know if it can be done in Poser5/6. The main characteristic of a ghost, other than some transpareny, is that the borders of the figure are not well defined, are vapourous! You can make a ghost with 1) backculling (not render back faces, don't look good for a ghost). 2) Inverse transparency (min 100% max 0% fallout 10) 3) Transparency index modulated by turbulence. With Poser4 you cannot use transparency maps, inverse transparency doesn't work with the map, I don't know if with Poser5/6 is the same. The most difficult part of a ghost is the hair.

Stupidity also evolves!