Just open up one scene and Import the other into it.
File --> Import --> Poser Document, and select the second scene.

(edit) - ummm, I was assuming that you have two Poser Scene files....

"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)