InTechSpot  

If you want to save videos from Google Video and you use Windows, you have the option to download them as GVI files and play with Google Video Player.

If you want to save the videos as AVI and view with any video player on any platform, use this bookmarklet: Google Videos As AVI. You can save it as a bookmark in your browser or drag and drop it to the link toolbar. Next time when you see a video you like on Google Video, click on the bookmarklet and you can save the video.

Explanation: The location for the AVI file can be found in the source of Google Video pages, but it's hidden for Windows users.

[Source : Google Operating System]