R1: what are you on about?
Old Biltong: how much RAM does the computer have? Latest Ubuntu, 8.04 (Hardy), needs a good 384MB to install. If it doesn't have this, and you definitely want Ubuntu, then try getting 6.06, which will install on less RAM, and can then be upgraded to 8.04 without too much effort.
Here's what you do:
1) Goto ubuntu.com, and download the version you want.
2) Burn this .iso file to a CD
3) Start up computer you want to use, and hit F2 or whatever it is to enter BIOS. Make sure that the CD drive is a boot option before the internet hard drive (else it'll always boot into Windows and never read the CD).
4) Put CD in machine, boot up, and it should hopefully present you with some options.
5) Choose to install Ubuntu. You'll be asked the odd question, like if the date is correct, and what username and password you want. After complete, it'll tell you to take out the CD and restart.
6) It should now boot into your Ubuntu system. Type in your username and password, and it'll get you in.
After doing this, you should connect to the internet (ethernet cable ideally) and download latest updates using Synaptic package manager (from administration menu).
It all sounds complicated, but it's pretty easy.
Don't forget that there's ubuntuforums.org, with a special section for absolute beginners. Worth signing up there to ask your questions, as they'll likely be more knowledgeable about it than those here.