Ubuntu is a Linux-based (Debian) operating system. It is quite light weight and has an interface that most of the "Windows" users will be familiar with.
It also bundles a Live-CD version, meaning you can just put your CD in and boot the computer into Linux without even having to install a single file on your hard disk drive.
Free CDs for Ubuntu can be ordered online from Ubuntu Shipit! It normally takes about a month or two for the CDs to reach here in India (sometimes even lesser :) )