i think it all depends on what games MS announces for launch..
the next generation graphics are really going to be unbelievably pretty... if RARE has something up its sleave that is amazing, I could see Xbox 2's flying off the shelves next christmas..
a large majority of hardcore xbox live users will most likely enjoy the xbox live system and decide to switch over.. so in america, there are like 750,000-1mil xbox live users? assume 100-500,000 of them are pretty into xbox live.. thats a good base of people that will immediately want to pick up xenon at launch...
but we'll see, alot can change, and 99% of the situation we dont even know yet.