If you save the file on the Mac to a PC formatted disk, and add the right extension (if needed, but most of the Poser stuff has extensions), it should be a PC file. The Mac will strip off the Macbinary header, that is the only real difference in PZ3 and OBJ files, I think. The library files (CR2, HR2, whatever) are another story though, I think it will still work (never tried it, though), but you will not have the icon, at least, MacConverter is best here.