There's no way to export the rig as actual geometry. Sorry.  You can make an approximation of the rig and export that but it won't, itself, be a working Poser rig. Even BodyStudio, our plugin to get from Poser to Max, Maya and C4D doesn't export the actual bones. It's simply not possible with the current version of Poser. Who knows what the future will hold though?

-T

PS. When last I looked BVH only exported the animation, not the rig. I may need to check that again, it doesn't come up much in tech support....