I've entered a new world on my Ubuntu box since I discovered virtual machines (VMs). I've installed VirtualBox (http://www.virtualbox.org/), and I am currently running a virtual version of Debian server so as to learn that environment, but I have tested Fedora as well, and have even installed Windows XP (though I need a product key to continue, and though I know there exist workarounds for this, I have a dual boot situation and don't really need it).
Using VirtualBox is simple and intuitive. You set the size of the virtual hard drive, set the RAM usage (which means you have to have enough memory on your computer to both run your normal OS and the virtual OS at the same time), then you just need a way to install. You can use a physical CD, since the VM makes use of your existing hardware if you configure it to, but you can also skip the step of burning a CD for your preferred Linux distribution since the VM can boot from an ISO image! You're really only limited by your hard drive space (typical Linux distros require 8 GB for a regular install) and your memory (which cuts into your normal OS performance, but I have 1.5 GB and am able to easily spare 512 MB for this). Of course the implications for this are enormous and have not been lost on the business world, particularly in the area of server virtualization.
For me, this is just giving me an opportunity to delve into other Linux distributions that I wouldn't wipe a hard drive for!