I use realplayer. Go to
http://my.real.com/?mode=rp and download the free basic realplayer. After installation, go back to youtube, find the video, play for a few seconds, place your mouse to the top right corner of the video and the download option box will be displayed. After you had clicked on it, a new realplayer page will display your download progress.
I would recommend you to exit your internet browser (IE or Firefox) so that the video downloading will go only into the realplayer folder and thus speed things up a bit, twice actually because your download don't need to be split into youtube as well. The video will be stored in document>video>realplayer download folder.
I had downloaded most of the X1 instruction video and save it for repeated viewing.