It is perfectly okay to install Poser9 into the Program Files folder under Win7.  However, your content runtime must be located outside that folder to properly change and save back content.  Your default should point the content folder towards My Documents as the share point for Poser Content.  I have this arrangement installed on my 64 bit Win 7 Pro computer with added external runtimes away from Program Files.  I have not experienced any problems with UAC yet.