You will have to buy a PCMCIA card or USB device which allows video to be recorded. [broken link removed]
You then connect the Scart socket of the Sky box to this unit, run what ever software came with to record video in mpeg format etc.
If the video picture rolls etc, there may be additional 'copy protection' added to it, in which case you need another device to go between the Sky box and PC to strip it from the video feed.
Towger.