If you are thinking about buying the cable supplied by sky store themselves which costs several quid extra, my advice to you and I'm sure other reviewers will vouch for is DON'T. This cable does exactly the same thing.
Although I already have a HD TV, I purchased this because I have suffered the purple screen of death that makes this box unwatchable. With this s-video cable I don't have this problem, just pure analogue stream with absolutely no disruption of viewing.
PLEASE NOTE : as a side effect of not using a hdmi cable, do not expect the picture to be HD quality, you will get a standard 16:9 picture with a slight picture noise, but with that aside the quality it produces is almost dvd and perfectly watchable.
I highly recommend