You must make sure the video is mp4 format for iPod. Here is a step by step guide about converting DVD, Videos, Flash and Youtube videos to iPod video,here is a step by step guide about how to use it
http://www.eztoosoft.com/mac-avi-to-ipod-converter.html
1. Open Eztoo AVI To iPod Converter For MAC, Click "Add" button to add video files.
2. Click "Encode' button, then wait a moment you'll get the new format video file.
Some useful information about iPod video you can get on the Apple official site:
http://www.apple.com
Also, you can search some other answer to solve your questions here.
http://answers.yahoo.com