Actually, if Nintendo gets their system out first, that'll be a big advantage. Most Xbox and PS2 owners aren't really loyalists, and they'll just get the next gen system that comes first. I've heard Sony has been having problems with the PS3, and that it may be a year late (not sure if this is old news, or even true, though), so the system will be just as powerful as the Nintendo system, but out a lot later.
A good starting line-up is also important. I'd suggest a Metroid game, since Prime was so popular, a mature game to attract the horomonal preteens that want them, a Super Smash Brothers just cuz it rocks, and another Nintendo franchise, probably Mario (and perhaps a new franchise). Also make it back compatible.