Going to Istanbul! Help! LOL

[Starwalker]

I'm going to Istanbul in a few hours for a week! and I have no idea what to do, or where to go. I just kinda randomly booked a flight and hotel a couple weeks back, and am meeting a couple of friends that have never been there either. I haven't even gotten a chance to plan anything besides accomdation...but I hear its an awesome city, vibrant, cultural, and there is a lot to do and see. I'd greatly appreciate if you guys could let me know, what are the best sites to see, best bars and clubs, resturants, to go to I'm gonna be staying near Taksim Square....they can be cheap or expensive, I'm game for anything.....and most importantly....what must I do before leaving!