Yes, in Poser you can add links to many Runtimes. Just go up to the top level in the Libraries palette, click the + sign at the bottom, and find your new Runtime folder (the one that was created when the products were installed). The name of the new Library in Poser will be the name of the PARENT folder of the new Runtime.

For example, I have folders called Main Library, V4.1 Library, V4.2 Library, A3 Library, etc, and each of those folders contains a separate Runtime.

I'm a bit lost as to why it won't open your files, I'm afraid, sorry.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)