I should have added this to the other entry.
If you really must make a prop instead of a figure (because you need smart-propping, or because it isn't worth rigging), the process is simple.
IMPORT the object you want. Poser can handle 3dmf, obj, some dxf, 3ds, all sorts of odd things. Obj seems to have the fewest surprises and is usually preferred.
SCALE and POSITION the object in Poser space. (And texture too, assuming you want to do it all in one).
SAVE to library using the handy "+" button.
Okay, if you want to be pro, you want to have external geometry. What does this mean? If you follow the steps above, Poser will put the mesh data into the pp2 file itself. (Or pz2, if you have compression turned on).
To make the mesh easier to access for editing, UVmapping, and other uses, you want it to be in the form of an .obj file in a different folder (the "geometry" folder) of your Runtime. To achieve this, you need two steps;
EDIT the pp2 in a text editor to take out all the mesh information and replace it with a pointer to the external geometry file (see my example in the entry "How to Make a Poser Prop.")
EXPORT the modified geometry from the workspace. Remember that you scaled and positioned your original mesh when you imported it into Poser? Those changes won't be saved unless you use the Export menu and have Poser create a new .obj file that reflects all those changes.