Berlin in one day, what to do, where to go?

I arrive in Berlin at 6pm on 26th in Tegel. I found 2 hostels, one in Mitten which sounds better and cheaper, but there's another one in Charlottenburg, very near to Zoo Station (Is ZooStation the train station for all eurail trains?). I have the night of 26th plus the whole day of 27th to get to know Berlin better.
I read somewhere they provide good tours of City (we can hop on a tram, buy a brochure explaining 11 places in Berlin, hop off anywhere we want then hop back on whenever we want). After the tour, could anyone suggest something interesting? I hope maybe to go to some disco or some hip clubs (but I'm not really the discoing type...), or maybe something else interesting someone could suggest? Thanks a lot. Oh yeah, Is Mitten far from Zoo Station (How to we get to the Station and price of the tram?)

Buy a one day ticket for 5.80鈧?for zones A and B on 27th. A single ticket costs 2.10鈧? is valid for two hours in one direction only. To get to Mitte from Zoo you need to catch a bus or go by Sbahn. Its a bit far to walk. From Zoo catch bus 100 to Alexander Platz then bus 200 back again. You can hop on and off at will and see most of the sites much more cheaply than using one of the tour buses. Alternatively, you can do a walking tour for about 12鈧? There will be brochures at your hotel reception to show where and when you meet them. These tours generally take four hours. Advice on places to eat can be found at "Eating and drinking in Berlin" at http://www.berlin-explored.com here is a link to some other hostels http://www.hostelbookers.com/hostels/ger...
BaxPax is directly opposite the G枚rlitzer Ubahnhof (At this point it is elevated above the road.) The area along Oranienstra脽e is full of interesting bars etc.

It is Mitte not Mitten
Zoo station is an important transport interchange but a brand new main railway station opened earlier this year (Hauptbahnhof)
When you arrive at Tegel you will need to catch a bus but I can't advise as to which without knowing your hotel/hostel. There is no Ubahn link at Tegel. Bus TXL goes to Alexanderplatz, mitte and bus X9 goes to Zoo.

I hope this helps and that you enjoy your stay in Berlin.

For the best hostel choice, look at user comments on hostel booking websites (hostels.com, hostelbookers.com etc.)

The hop-on-hop-off buses are rather expensive. For the main tourist attractions (and if you have a mp3 player), try the free mp3 audioguide on Berlin (and print out the map)

The Berlin iAudioguide.com currently covers:
1 Charlottenburg Castle 2 Victory Column 3 The Building of the German Chancellery 4 Reichstag 5 Brandenburger Gate 6 Holocaust Monument 7 Potsdamer Platz 8 Checkpoint Charlie 9 Gendarmenmarkt 10 Berlin Dome 11 Alexanderplatz and TV Tower

Lot of good advice came from John b already.

Kreuzberg and Prenzlauer Berg are "hip" areas, where you will find clubs and places to go to. Never rule out something that lies in a so-called quiet neighbourhood, though. Wilmersdorf and Dahlem do have some cool places!
Depending on your taste, you can go to raves and "private" clubs, but need to check links how to get there. It is best to have someone local to help you with that.

There are TIP( http://www.tip-berlin.de ), PRINZ (http://www.prinz.de/berlin.html) and Zitty ( http://www.zitty.de ) as magazines to help you with announcements, even without knowledge of the German language you should be able to figure out whether there is a concert of interest to you or a location you may want to go to for partying.

Have fun

Personally I would prefer the hostel in Berlin-Mitte (it might be a one near "Rosenthaler Platz" - that's a nice one), cause the main sights are in Mitte and it's the district best representing whole Berlin. If the one near Zoo Station is the A&O Hostel: It's not a very nice one...

The main sights are located mainly at or near the street "Unter Den Linden" (Stations Friedrichstra脽e and Alexanderplatz). It's a nice walk when you hop off Alexanderplatz or Hackescher Markt station and walk into the direction of the bigger landmarks (e.g. churches, towers...)

Taking a trip with the Bus 100 or 200 is a nice option if you don't have that much time, they cross many of the main attractions and with a day ticket you can hop on and off whenever you see something interesting. This plus a visit of gendarmenmarkt, friedrichstra脽e, oranienburger str. and the surrounding area to hackescher markt and a walk from hauptbahnhof to brandenburger tor will fill a day easily. If you're going to kreuzberg, visit bergmannstr. and oranienstr. and wrangelstr./schlesisches ufer. In prenzlauer berg especially area around station eberswalder str. is interesting (oderberger str. and kastanienallee). In friedrichshain the street for tourists is simon-dach-str. (filled with bars and restaurants).
Regarding clubbing: On 26th (DEC) there are some nice parties - if you are into guitar music you might visit the sophienclub or the magnet. Nice is also visiting the Zapata in the famous and touristy Tacheles, there the evening is more beat-focussed. Another electronic music party is at the famous icon.
A bit newer and a mixture of bar, lounge and club is the gl眉hlampe in friedrichshain/warschauer str.