I commented in http://www.flyertalk.com/forum/europ...-marriott.html but my comment was removed because the thread is from 2004.

A good way to get to the Berlin Marriott from Tegel airport (TXL) is to take the TXL bus. Just follow the "bus" signs at Tegel, go outside and go to the right to platform 2. Then take TXL and exit at the stop Brandenburger Tor (one stop before Unter den Linden). From there, take the S-Bahn (S1, S2 or S25) to Potsdamer Platz.