While Nintendo has great upside I love the Xbox for HALO which is the best game IN THE FREAKING WORLD end of discussion!
Halo 2 is coming out next spring and Halo for PC is out now.
All platforms have their upsides and downsides but I love XBOX's original Buffy the Vampire Slayer and HALO for XBOX the most!
If you go for Nintendo GC at least buy the PC version of HALO you will not believe how GREAT a game can be even running on a Dell computer(XBOX would give you a much better performance)!
Peace,
Tony