One of the best desktop video players is VLC Media players available at http://www.videolan.org/. I would recommend, if you haven't already done so, pay the extra money (usually under $100) for Corel VideoStudio Ultimate, which will allow you to edit the downloaded videos.
For downloading YouTube videos, in the ADDRESS area of your browser, replace youtube.com with youtu10.com (just replace "be" to "10"), and press enter. You will be taken to the download screen and follow the instructions to download any YouTube video.
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