Having hacked Dynamic hair to death, I can say that Ajax is right, and also you'll want to hunt up a little posting from me in the poser technical forum here and int he Poser 5 forums at RDNA and Poser Pros -- a great deal of that slowdown in render time is due to the dynamics being stored. The P5 hair fix will tell you how to fix that, and believe me -- you'll see some serious changes in your hair rendering time. (for the better, I might add)

thou and I, my friend, can, in the most flunkey world, make, each of us, one non-flunkey, one hero, if we like: that will be two heroes to begin with. (Carlyle)