Check the Ubuntu.com page
https://help.ubuntu.com/community/Installation/SystemRequirements
and the Ubuntu Forums (another good place to get info on Ubuntu)
http://ubuntuforums.org/showthread.php?t=24890

The software you DL and burn to a CD, the CD is then bootable with a copy of
Ubuntu that you can run straight from the CD on your computer. No
installation to the harddrive. That is providing you computer CAN run
Ubuntu. Note: Running from the CD WILL be much slower because CDs are much
slower than HDs.

Get Ubuntu here
http://www.ubuntu.com/getubuntu