Poser Physics requires P6 SR2 to function correctly. However. What you -could- do is build your animation in P6 (just the figure and motions), export the animation as a BVH file, load the character(s), import the BVH, then do the hair and cloth dynamics in P5 and export from there. It adds a couple of steps, but (a) gets you some use out of P6, and (b) lets you have access to the physics simulations. Since both P5 and P6 have the selectable runtime feature, you wouldn't need to duplicate your runtime. And it would also let you do some tweaking on your Poser setups; if P6 is just for keyframing and physics, there's a lot of stuff you could hide and ignore, giving you more screen area to work in.