First of all, don't use 3DS; use Wavefront OBJ format which is what Poser understands best. Depending on your version of Max, you may need the Habware import/export plugins; later versions can do it unaided. Most modellers scale up before import into Max, and scale down again after export; I don't think Max works very well at tiny scales. It's also best to use the figure mesh direct from the Geometries folder, since that is guaranteed to be completely unposed. If you export, you have to be sure to zero everything, although this is more important for conforming clothes than dynamic ones. The other thing to remember when importing stuff into Poser which is supposed to be the right size (as it will be if you modelled around a Poser mesh and matched your scale up/down correctly), is to uncheck all the boxes on the import dialogue. When it says "100% of standard figure size" it will actually rescale your import to be the height of a standard figure.