The alternative as kmote mentioned is to download a Linux "distro" (means distribution).
Download Ubuntu | Ubuntu
Then using a program such as ImgBurn
, you can burn it to a CD. Then you would make the CDRom drive top priority in the boot list at the system setup screen. So when you boot up the computer it will show in this case, Ubuntu. Enter English for the language, hit the top option (to run it as a live CD and not install it), and then we can help you from there.
Oh, and kmote is spot on ! Back up back up back up !