Transferring individual OE5 folders from one PC to another?

[Aurelius]

I tried to copy or import the Inbox and Sent-items folders from my old machine to the new one. Since I wish to keep my new mail messages and also have access to the old, I renamed those folders to Old-inbox.dbx and Old-Sent.dbx and then tried to import them or copy them. However, when I open Outlook Express I don't see them!
Is there a way to import old message folders (without destroying the new)?
Win98SE, OE5.

Thanks for any tips!