Do you know where in Berlin you're staying yet? It's an awesome city with loads to see and do. The buses and u-bahns are great for getting around and fairly cheap. Some of the main sites to see include the Olympic Stadium, The Reichstag (free entry to go up into the dome), Brandenburg Tor, Seigessaule (Victory Column), Kaiser Wilhelm Church and Potsdamer Platz. The Checkpoint Charlie Museum is also really interesting but it's got so much stuff in it now that it does get a bit too much to take in. Foodwise, the best steak I've ever had was at Block Haus on Karl-Liebknect Strasse (near Alexanderplatz). The restaurant up the top of the Fernsehturm (tv tower) rotates and has amazing views of the city and Aigner near Gendarmenmarkt is a smart restaurant serving good food.
I could rave all day about Berlin so of you want to know anything else give me a shout