I think there are Poser 5 and 6 Dynamic Hair products ? 

The problem is, as I have found out, you need a scalp base to grow the hair from. 

That either means you get the permission  of the figure's creator to extract the scalp mesh, or you get a royalty-free scalp base which you can re-distribute with your dynamic hair files.  Some creators may take the view that "body-bagging" a scalp mesh may be an infringement of their work, so one must always check with source.

Poser 7 provides royalty-free scalps, and I think Netherworks and PhilC have scalp meshes, and there are a few others, but I can't recall off the top of my head right now.

Eternal Hobbyist