I moved several of my small virtual machines (VM's) from my old server to the new HP server. The process was pretty smooth. Just copy the entire VM folder (which was about 4GB) to the new machine; load it to VMWare Server's inventory list; start it, and voila! The only thing that took long was the physical moving of the VM folder.
I can imagine putting all VM's in a shared storage device, or SAN, can make the whole process so much simpler. If you have several servers running VMWare, you can just un-register it from one server, and register it to another, to "move" it easily across your server farm.