Its not server virtualization as such that I am after. In university we used a piece of software for digital electronics that allowed us to add components and create test circuits. Is there anything like that for networks? i.e. start with a router, drop in a firewall a DC etc? If you wanted to plan your network topology is there anything out there you could simulate it?
I am using packettracer which is part of my CCNA course.. only deals with cisco stuff of course but you can build massive networks with it.
Very good for learning about cisco stuff.