Importing mail from old server

I know the topic is cinda short but this is probably something simple but i just cint find the answer anywhere.

Im running a standard mail server on OS X 10.4.6 what i now need to do is to import some mailboxes into existing users on our server.
The reason is that the users only use webmail and they switched to us about 2 months ago and their old provider sent us the maildirs from their courir-imap server.

Anyone have any ideas how to do this or is better friends with google than i am plz let me know.

Dagfinn Kolstad