I apologize for not being specific, but I'm sitting at a computer without Netscape.
Find the user name on the 4.7 computer.
Copy the mail folder(s) that is/are below that user name. It will be easy to tell the name of the folder, because it should have subdirectories for each folder created in Netscape messenger.
Paste the folder structure as another subdirector under the user's mail folder on the 7.0 computer.
When you open Netscape 7, there should be a folder structure similar to the one on the 4.7 machine with all the messages in it.
Now if you want to sync the folders, that is up to someone else to answer.