I have the same situation as pekay -- i have my .VirtualBox folder on an external hd, and I thought this would be enough to save a snapshot on one host and open on another host. On the second host, I've set the HardDrives, Machines, and Snapshots preferences to the folders on my external drive, but the snapshots saved on the first host aren't shown.
vbox4me2, what are the xml files you say need to be copied, and where are they in a default install?
I'm using VB2.2.4 on the second host. There are 3 snapshot files at G:\.VirtualBox\Machines\Win7RCPortable\Snapshots on my external drive, and Settings | General | Advanced | Snapshot folder is set to that path.