Composite to S-video

I found something I think to be a composite-to-S Video cable. One end has a yellow recieving port/hole, the other end is a plug with an s-video configuration connected by a narrow cable. I checked only to find such cables, though ones that didn't look as dinky as this one, sell for over a hundred bucks. I was just thinking: From what I've read of the posts, all you guys do to make s video cables is simply send the corresponding connections to each of the plugs on an s-video (ok, not so simple, I can't do it, but you know what I mean). I figure that's what my little doodad does too, without all the work. Am I wrong? Is my little doodad a pos? I'm gonna use it anyway to hook my genny because the reciever only has s video ports left. Thanks guys.
well it certainly won't improve your quality (at least not noticable), basically the video date would go like this:

Genesis' VDP (RGB) -> Genesis AV port (composite) -> circuitry that splits composite into Y/C -> S-video

As you can see that's far from optimal...
I got one of these things from Radio Shack. It's a small 1.5" black plastic tube with a composite plug on one end and a svideo plug on the other. I only use it when I have no choice but use composite with my laptop, otherwise I stick to svideo.

It DOES NOT improve the quality of the video in anyway when going from composite to svideo. It does work both ways though so the you can convert composite -> svideo or svideo -> composite. Converting svideo to composite does have a slight improvement over using straight composite. But not very much.