In case anyone is still paying attention to this thread, I got around to just copying Poser 5 over.

Everything is nice and snappy right now. My belief is that the registry entries (and more specifically, I'm guessing file/extension entriess) are the culprit. Considering my Poser 4 is not installed but is copied over in a similar manner, I have no Poser registry entries. Which makes me hazard a guess that people could get rid of all Poser related registry entries and see a performance increase.

I am not suggesting anyone do that. Your problem if you do, but it'd be an interesting experiment for those brave enough to see.

So, in the end, I think the blame falls on Microsoft here. Registry bloating is primarily Windows's fault for their code, though it doesn't help when every program puts in a billion entries. Then again, I may be completely off base on my guess, but my system is better for not having installed either program. Gotta love programs that work without registry entries.