When I asked MS, they said installation of Programs at the Root Level is not recommended and you may encounter unexpected errors. This was for Windows 7 64. This was in June. I did not ask why, but I also believe if you have UAC off this is not an issue, but they also do not recommend turning UAC off either, and if you use the default installation for Poser 8 or Poser Pro *(Shared Folders for Content) you also will not have issues.

ratscloset
aka John