Wow I'm surprised Poser 4 works on Win 7. I stuck with Poser Pro (7) for quite a while. I'm still on 2014 because it is the best version for animation as far as I have experienced. The latest stuff is amazing too but there are just some bugs and things that annoy the crap out of me enough to not update just yet. Hope it gets worked out.
If you're that hardcore about sticking to the old stuff you should look into preserving an old PC. I know people do it. Not certain how myself.

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My most recent Poser animation:
Previs Dummies 2