C12G recently released a Sandbox Appliance for VMware and now they are doing the same for KVM. The appliance image is already in its OpenNebula marketplace but hold your horses and don’t download it just yet. Head to the documentation and download the script that will be used to configure your machines, download the image and start it up.
The requirements now are at least a couple of machines with Ubuntu Server 12.04 64 bit. The CPU should support hardware virtualization as we are using KVM here. It is based on the VMware appliance so you’ll be able to develop in it if you need as all the libraries needed for compilation are already there.