How do you record sounds from your computer?

i dont have a mic .
iwant to record striahgt from the computer.
example : when watching a video when you record ; you can hear the sound from the video once your done.

Replay Music by Applian: http://www.applian.com/replay-music

You can try this way:
http://www.capturestreamingaudio.net/record-sound-from-website.html