There are lot of software available to download you tube videos. For those who don’t want to download and install any software for security reasons, the best way to download you tube video is to copy URL of the page that has the video you want to download. Then visit the website http://keepvid.com and paste the URL in the Text box provided and just click ‘Download’.
You have provision to download the video in various formats like MP4, FLV, 3GP, MP3
Few more websites with provision to download you tube video without installing any Software