It's entirely too hard to say for sure what the Legend of Zelda: The Wind Waker sales will do, but if Super Smash Brothers: Melee is any indication, it will continue to sell. Unlike Metroid Prime, Zelda has a main mascot appeal to it, and unlike Super Mario Sunshine, as long as it truly delivers, it will have some amount of staying power.
However, it occurs to me that everybody and his brother that owns a Gamecube is preordering Zelda, namely for the bonus disc. Frankly, I'm surprised if Nintendo shipped 250,000 bonus discs. I think Ocarina of Time could sell 3,000,000 copies on the Gamecube, too.
If there are enough preorders, it will be hard for Zelda to keep up that kind of pace. However, I do think the amount of consoles sold will spike in response to the release. The increase will be the factor. With only a small climb in console sales, Wind Waker should sell approximately 1,500,000 to 2,000,000 copies in all. If good number of consoles move, then it could sell 3,000,000 no sweat. If Wind Waker caused the kind of craze Ocarina of Time did, then it would probably tie or break its record, but I don't think that will happen. It's just not likely.