There. Box reinstalled, OpenVZ containers for web, mail and DNS, moved all the important things from the old production box and everything is working very well so far.
I have just copied all of ISPConfig's settings (I re-entered everything in the ISPConfig control panel manually!)
One thing left: I want to restore the old passwords for email, web and so forth. How can I do that? I have the old server's database dumps, can I restore the password only in the master or should this also be done on the slaves? It is very important for one user because I don't have any clue how to reach the user other than via email hosted by me :-)
(You know, as an aside, an elaborate import/export would be so very nice to have.. is this something on the roadmap?)