www.CatchVideo.net enables you to convert YouTube videos into any number of
different video formats and then to download these to your computer. It's
FREE and very simple to use.

Once on your computer you can view or copy the files to any number of
devices including other computers, mobile phones and literally any device
that plays video. You can even email the downloaded videos to your friends.

There is a an addon in FireFox that can capture YouTube videos.
Although, I can recall at least one time where it wasn't successful,
so I stopped using it. Actually, I was having a BSOD problem that I
traced back to one of the FireFox addons/plugins, so I just
uninstalled everything.