The Wii component cable only smooths out some of the jagged edges on HD TV's (and I think it might reduce input lag), but it doesn't actually make the games "HD". They just look marginally better than they usually do on HD TV's. So no, the game isn't HD, and neither is the Wii.
The cables actually just prevent the TV from "upscaling" the image by sending it in the native format instead of the legacy image older consoles put out. So, it reduces the time it takes for a TV to render a frame, and presents a clearer image. However, it still won't be HD, as the source image isn't HD. The Wii is not HD capable and therefore will not normally output HD images. There is no way to force a standard game to run in HD on it as of this time, and it's very doubtful there ever will be one. Certainly, the result wouldn't be pretty.
So, no, this game, and every other wii game, is not HD.
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The component cables are a must have with larger TVs. I didn't notice a huge difference with a 37 inch TV, but the difference is night and day on my 50 inch. I suppoes it's possible my 50 inch does a much better job upscaling 480p than 480i though.