To download a "YouTube" video to your PC, just copy the URL of desired file which looks like 
this  :  

Now, paste this kind of URL into the textbox below and press "Get Video" button. After few moments, a download link will appear under the box below. Right click on this download link by mouse and select "File Save As" or "Save Link As" options  which will open "Save As" dialogue box.You will see it's default name as "get_video.php". Just RENAME it with your suggested name alongwith it's file extension like "abc.flv" and click "Save" button which will start the downloading process! 

The downloaded video file is a FLASH VIDEO (flv) file.

To play this file on your PC, you need to install VLC Media Player on your PC.