Best answer as chosen by user wpgwpg: Re: download Ubuntu
http://www.ubuntu.com/download/desktop is the place to start.
Then follow the documentation to burn it on an iso, and read the next page, It says:
Put the Ubuntu DVD into the DVD-drive. Restart your computer. You should see a welcome screen prompting you to choose your language and giving you the option to install Ubuntu or try it from the DVD.
As long as you don't install it, it won't touch your hard disk.