Then I'm not sure I understand your problem at all, Andy. You say the needles on Walli's trees don't use image mapping, and they are each six sided polygons per needle, is that what you're saying? Surely the trees would soon become pretty unmanageable if every single needle on every single twig were an object in itself!
I really can't see that being the case, I can even see repeating needles in the hi-res renders the NWDA guys posted to show off these trees, although, I'm often very wrong. I don't believe that these trees use no image maps for the needles and that you are, indeed, seeing the mesh in your 3D preview before needle alpha has been taken into account.