What is Linux ?  its an operating system, a bit like windows, but is totally free !
No need for anti-virus software, there are no viruses for Linux !
Open Office is a free office suite, fully Microsoft compatible.
There are 1000's of free software packages available to download.
Music, movie players, web editors, games, and loads more.

Ubuntu linux

Download Ubuntu here      Documentation     Ubuntu Forums     Complete guide to Linux  FREE 

Ubuntu comes as a Live CD. Download Ubuntu, burn it onto a CD,
put the CD in your drive and boot. Ubuntu will run from the CD
so you can try it without installing!  A nice safe way to try a new OS.

Puppy Linux - another FREE operating system
great for new and older computers.

Get the latest version of Debian.