I am running a multiserver setup and need to move some of the servers (mail and db). I took a look at this : http://www.howtoforge.com/forums/showthread.php?t=2717 but I am not sure if this can be used for a multiserver setup. My servers are running Debian Lenny. The new setup will be on a VirtualBox with Bridged Network, but still Debian Lenny. I am using ISPonfig 3.0.4.1 Hope someone can come with a good guide or hints.
Have you considered to make a system image with a linux backup software or dd and convert this into a VM? If I remember correctly, there is a utility called p2v for virtualbox to do this.