Ubuntu is a linux distribution that has a GUI very similar to Windows, therefore should be easy to use for novices( like myself, for instance; I've been using it only for a few months and I have no issues with it). And yes, a desktop should work fine as well.
You can download and burn a bootable CD with Ubuntu on it and run it from the CD; that way, you don't need to install it on your computer, just select the CD-Rom as the first bootable device in BIOS.