Hello
I sink the easiest way is to use an TimeCapsule with an TimeMaschine Backup from the Server.
When you Boot VM from an OS X installer CD, you can youse TimeMaschine Restore to Connect to the TimeCapsule.
I Test it with en Snow Leopard Server. The Copy works, but i can´t boot the server because there is no Support for Snow Leopard on Parallels Server for Mac.
Regards
Florian