There is nifty free and open source tools out there which can be used to download

This tool is created using Python programming language and it’s called youtube-dl

Screeshot of youtube-dl in action

To use it you must do the following

  1. Then download and install Python (What is Python?). Direct link for Python Windows Installer for XP/Vista
  2. Get it from http://www.arrakis.es/~rggi3/youtube-dl/. Direct link to download youtube-dl here (Right click and save as)
  3. Press Windows Key + R (Win+R) and key in cmd (Without quote) and then press enter
  4. Type in  cd [Path to your downloaded youtube-dl.txt file] press enter  e.g. cd c:downloads
  5. Then key in c:\Python26python.exe youtube-dl.txt [PASTE YOUTUBE VIDEO URL HERE]
    Press enter and it will starts to download shortly
    Screenshot on how to use youtube-dl

from screenshot above you can find the *.flv file in c:downloads

you can then dowload http://www.videolan.org/vlc/ to play*.flv file