Is there public transportation from Brandenburg Airport to our hotel located in the Potsdamer Platz section of Berlin. If not does anyone have an idea of how much a taxi would cost.
Current estimates are that Brandenburg's opening has been delayed until at least March 2013. This may affect your plans.
All the Berlin airports have websites that list arrival and departure info from and into the city. Brandenburg, scheduled to open on March 17, 2013 will have a train right under the terminal taking you downtown in 30 min. and also a subway (U-bahn = U for Untergrund/under ground). This is the website: http://ber.berlin-airport.de/. It says the website will be updated as the opening time comes closer. An- und Abreise zum Flughafen will give you the ground transportation info. It also tells you how to connect further once you're downtown.
If you are going to be in Berlin before the opening of Brandenburg and are flying into Tegel, there is a bus that runs from Tegel along Unter den Linden to Alexanderplatz. I think the bus ticket is only a couple of euros.
Brandenburg Airport is currently severely delayed and you may end up flying into one of the older aiports. If, as will probably occur, you end up flying into Tegel, your best route is to take the TXl bus to Unter den Linden S-Bahn (underground local railway) station and take the train from there to Potsdamer Platz. If you actually do fly into Brandenburg Airport, or into the older current airport Schoenefeld that is nearby, you should take a train from the airport station to Friedrichstrasse station and take the S-Bahn from there to Potsdamer Platz.