VMware Player

You can use VMware Player to simulate and run virtual machines on your computer. You can download it from here http://www.vmware.com/download/player/. You can also get virtual appliances (machines) from VMware at this link http://www.vmware.com/appliances. Depending on what kind of appliance you need, you can download, install it and run it off your desktop. This is a very good way to learn new technologies and get hands on experience.

Just one plus point over VirtualBox. No CPU hogging!