I have found the YouTube Downloader program to be most suitable for this task on the Windows operating system.
Here is a screen capture of the interface. All you need to do is enter the URL of the video, choose a destination folder and optionally select a different format. MP4 is useful for iPod and AVI is a regular Windows format. The default format of YouTube videos is Flash video (FLV).
The program can be downloaded from this link. Warning! When you install the software, choose the custom installation, read the prompts carefully and deselect all of the other programs and modifications to your browser. You don’t need these!