Start by downloading Handbrake. The latest version works on Mac OS X 10.5, Windows 2000/XP/Vista, and Linux. Previous versions work on other operating systems, but are no longer supported.
Once you've installed Handbrake, get the DVD you want to add to your iPod and insert it into your computer. Depending on how your computer is configured, your DVD player software may try to launch automatically. If it does, quit it and launch Handbrake instead.