There are many posts outlining the problems with Windows 7, Program Files folder and UAC.  In which case, I am assuming that you installed Poser 8 into Program Files.  Aside from adjusting UAC security to a lower setting (not highly recommended), it would have been best to install your content in a shared folder, like My Documents, which bypasses the security restrictions set up by Windows.  Most DAZ installers will look for a Poser.exe file which you do have; only the pro versions will have installation difficulties.