I finally got a component cable for the original Xbox from MVS through Amazon. The problem, as described earlier was that I was rather naively searching for the word 'component' which doesn't appear in the name of this item.

I'm glad to report the difference in picture quality is astounding. I can actually see jaggies! And the colour depth is like going from the built-in speakers on a portable telly to an amplified 2.1 system. A tenner including delivery.