I have the hidef pack also, they come with the necessary cables? Why would u buy cables if you already bought the msft hidef pack? To me it looks good enough. I cant really imagine it would look that much better if you bought another brand. Get the msft hidef pack and if u dont like it then go out and buy another set of component cables.
IMO, you won't be able to tell much difference, if any, when going from S-video to component video unless your TV can do progressive scan. I also have quite a few brands of component video cables in use at my house. I have the standard cables that come with the XBOX, Monster Cables, Acoustic Research, Better Cables, Nintendo brand for the GC, and even some Pelican brand component video cables that I used for while with my PS2. I don't see one bit of difference between any of them. I guess that would depend highly on whether you have problems with interference, apparently I do not. YMMV.
I actually saw last night a 9ft component cable which looks real good at Super Wal Mart for $22 and some change. I thought that was about the cheapest I've seen...