If you can watch it, you can download it!

At least you can with the AntVideoDownloader, a plug-in for Firefox and Internet Explorer.  When installed, it adds an icon in the corner of your browser.  When you are on a site that plays any kind of video, simply click on the Ant icon and it will download the video to your hard drive, no questions asked.  There will be an
"Ant Videos" folder in your downloads folder and that is where your video will be.  Quite simple, now you can download all the cat videos from Youtube that you desire!