Go to the top of your Poser folders in the library, then click the '+' button at the bottom to add your runtime.  Navigate to your runtime folder in P7.  Word of caution: huge runtimes are not good for Poser of any version.  The time it takes to configure the library can crash your system.  The recommendation is to divide your huge runtime into organized, smaller folders for easy access.

Follow the thread to a previous post:
http://www.renderosity.com/mod/forumpro/showthread.php?thread_id=2751008