Microsoft don't produce the old xbox anymore, and iirc they don't put out new titles for it, and their support will be very very limited.
99.9% of Live users wanted to be able to move as seamlessly as possible from the xbox to the xbox 360, and MS are trying to use Live on the PC too. The only way to do that is 1 subscription type. It makes a lot of sense.
If not people like yourself would get a xbox, take out an xbox Live sub, then 3 months later decide you want a 360, then bitch about not being able to use your same logon.
They want a unified service, gamers want a unified service, we have a unified service. It is not often you will find me sticking up for MS but this is one of the times i think they are 100% spot on.
Ask for a 2 month trial code on here, i am sure someone will have one laying around. I will even check when i get home to see if the ones i have have expired, if not, you are welcome to it.