If I were you I would go to Ubuntu's website and download the latest version. Burn it to a disk and instead of installing it, run it "live".
During the installation process, you will be asked to install or try it. If you try it, you will run the operating system from the CD/DVD instead of installing it. Nothing will be saved, but you will be able to try it without wiping your windows installation.
This can be done with most all distributions of Linux. I'd say try as many of them as you can stand!