Ubuntu 8.10 i386 DVD is useful for almost all PCs. This includes most machines with Intel/AMD/etc type processors and almost all computers that run Microsoft Windows, as well as newer Apple Macintosh systems based on Intel processors. Choose this if you are at all unsure.
Ubuntu 8.10 i386 DVD allows you either to install Ubuntu permanently on a computer, or (by entering 'live' at the boot prompt) to try Ubuntu without changing your computer at all.

About Ubuntu

Ubuntu is a computer operating system based on the Debian GNU/Linux distribution. It is named after the Southern African ethical ideology Ubuntu ("humanity towards others")and is distributed as free and open source software with additional proprietary software available. Ubuntu provides an up-to-date, stable operating system for the average user, with a strong focus on usability and ease of installation. Web statistics from late 2009 suggest that Ubuntu's share of Linux desktop usage is between 40 and 50%.