I'm looking at the feasibility of providing remote access to multiple virtual machines. The VMs themselves will provide user desktops.

To make best use of the available resources, I'd like the VMs to hibernate when the user disconnects. Which implies being able to start them up when a user connects. Ideally each user would 'own' a VM image - but if not then I'd require that the session was terminated. Obviously this would require the remote access protocol to be tied into the VM management. Is there anything out there to provide such functionality?

(extra credit for open protocols! ;)