If you have obtained a boot disk for Ubuntu, then all you have to do is put the disk in the drive and then restart your computer. A menu will come up that gives you the option of selecting a boot device (F or entering Setup (F1). Choose "Select A Boot Device", and then find your CD drive in the options. Then just wait, until a menu pops up, and just go to "boot Ubuntu without making changes to the computer." Wait for it to load, and it will automatically load you as a "Super Administrator." Now, just click on "Applications" at the top left of the screen. Click on "Accessories," and then click on "Terminal." Now just type in "sudo gparted", and this will bring up a partitioning tool, just click on it.