Eventhough turning down UAC will remedy the issue, it is not the most recommended method.  When installing PP2012, you are given a option where to place your runtime content; the default will be a specific share folder under Documents.  This is the preferred option for Vista/W7 OS, and I would imagine also for W8.  Typically, DAZ installers will search for Poser.exe; you can override this be either creating a dummy file as Basic detailed, or manually selecting where you want to deposit your content.  Don't allow the installer to automatically search for the Poser executable.