There are 3 basic ways to do this;

1) Realplayer Downloader:

The best one and its free and dead simple to use.

2) Record Youtube Videos with TubeZen

You simply paste the youtube video link into the site pick what video format you then download it to your PC.  Its simple and very easy to use.

3) Recording Video Streams:

Sometimes youll want to record a “Live Stream” of a tv show or webcam. The best and easiest way to do this is a program called “WM Recorder 14”. The demo version lets you try it out and you can save 5 mins of almost any live stream on the web. To record more than that you will need to pay for the full version.