All you need is a component cable to get 480p (progressive scan) out of it, which apparently is coming standard with the Wii. You won't get a high definition picture from it, the Wii isn't supporting that. 480p, without going into too much detail, means you'll get a visibly cleaner and slightly sharper image than 480i though, which is what PAL Gamecubes use.
Short answer: as long as you have a component cable you'll get the best out of it.