The Verdict
This is easy, and you as the reader should already know my verdict. While both systems handle HDTV quite nicely, and both support Widescreen very well, the XBOX has taken the Gamecube to the cleaners when it comes to quality. The XBOX itself has an option in the main menu for "Widescreen", thus putting all games in the 16:9 aspect we love so much. The Gamecube has nothing but a nasty stretch function that leaves it up to the games to come up with the fix. Unfortunately, Metroid Prime only impressed me as it came to the Widescreen HD fix, which is not too suprising.
Overall, the XBOX wins in the HD/Widescreen fight. I would reccomend, however, you don't take this as a "GO GET THIS SYSTEM" review- the Gamecube has many games that are must-plays, and just because it stretches on your screen doesn't mean that it doesnt look good on it. The same applies to the PS2 (Though the PS2 wasn't made for such HD-ness, which is why I didn't review it). In any case, the XBOX is still the clear winner.