Poser 7 will not replace Poser 6.   The parent directory is called "e frontier", rather than "Curious Labs", and the home directory itself is called "Poser 7".

I don't have Vista, so I can't comment on that, but which utility do you use to unzip files?     On XP, I don't use the internal zip/unzip function, but always use WinRAR.   Can you give any details of the problems?