ticket pick up at Beijing airport ?

I'm aiming to buy bullet tickets online for Xi'an and pick them up when I arrive in Beijing. My question is - does the airport (BCIA) have a train office where I can collect them, or will I have to go to a railway station ? I've seen a website which suggests I can pick up tickets in terminal 3 but I don't know whether the website is up to date or not !

RIchard