I don't know of a tutorial specifically geared for this, probably because your going to need a 3d modelling program of of some sort and the instructions would be very specific to that particular program.

Basically you'd need to export the pieces you want from one model as seperate object files from poser, then combine the meshes in the 3d modeling program of your chosing, reimport back to poser and use the setup room to re-rig the new figure.

Not terribly complicated overall, but a great deal of the instructions involved would be how to join the two alternate meshes in the 3d modeling program itself, so I don't know if anyone has written a tutorial for your specific modeller of  preference or not.

Stepdad