1) Download and install Firefox browser (if not already installed) https://www.mozilla.org/en-US/firefox/new/
2) Once installed goto YouTube and try to watch the video. Most likely you could not. You may have gotten an error to install Adobe Flash Player. Useing the link on YouTube that shows up where the video should hve been, click it. Follow the instructions on Adobe's site to install. Pay attention to the cebter advert box, it will hve checkmarks to install 3rd party software, uncheck them if you do not want them installed. The only thing that downloaded was the Internet download installer, so goto your download folder and double click it and follow instructions. Once installed return to Firefox and the videos on YouTube now work.
A side note. Firefox may require your permission to run Flash on each new site, why? Adobe had their entire stack of software code compromised and released into the wild, it is therefore by logic unsfe, the down side, much of the Internet uses Adobe, at least until HTML5 is standard across all platforms.
3) From the installed Firefox Bookmarks click on Addons
4) At the Firefox addon page search for "Videodownloader" all one word without quotes. It looks like three balls, red, yellow and blue I think. Three balls nevertheless.
5) When found click install to the right.
6) Restart Firefox if prompted
7) Return to YouTube and the video "Seven Brides for Seven Brothers" and allow the video to start playing. Once it has started look for the different color balls on the Firefox toolbar, to the right or left and sometimes under the video. If the balls are spinning that means you can download the video.
8) Click the aarow next to the balls and choose "Medimum .4mp" Few home users will have the codex install to run the other formats.
9) The video will download to your profile on your computer to a folder named dwhelper.
That's it you have the video.