Further to my earlier post (Virtual Server 2005)about problems moving virtual images with saved states onto a rebuilt server (and also onto a new server) through some experimentation I found that if I rename the .vsv file accompanying the .vhd and .vmc I am able to add the virtual image successfully.

Microsoft has a technet article explaining things in more detail on the Microsoft site here. Essentially the vsv is the saved-state file, more details of all the files and folders can be obtained on the technet website here.