If your Gamecube doesn't have the digital port on the back, you won't be able to use the component cables.
Even if it does, be prepared to pay out the nose for the cables - they're out of production and sell at a grossly inflated price on eBay. I ended up selling mine (along with my cube) since they're going for twice what I paid originally (and they're going to be worthless in about 6 months anyway.)