PoserPro was the first version of Poser to have the default runtime install location at users/public.
Alll previous versions have their runtime install locations at Program Files.
In that case you have to turn off UAC in Vista or Windows 7 if you want to add files to the local runtime. Vista and Windows 7 simply do not like to have data files written to the program files folder if the User Account Control is turned on. It will work however with the proper permissions on.

Using the documents (or other) folder for the runtime has no further impact and is a good way to avoid (future) problems.