Backup stored messages

[Karjala]

Hi

How does one backup e-mail messages stored in Cyrus IMAP's mailboxes?

Which directories to copy, and do I simply overwrite afterwards or is 
there some procedure I should follow? Can I store the accounts and 
passwords or do I need to create them with cyradm afterwards?

I'm using Debian stable, with Cyrus 1.5.19, but can upgrade to Cyrus 2.1 
if needed.

Thanks,
 - K.