The Turkish police are generally quite friendly to foreigners. The most important thing is to be helpful and polite. It's likely you will end up waiting a good long while because they will need to track down a certified translator in order to take your statement.
You should call the US embassy or consulate. Unlike the movies, they won't send anyone out, but they will have a list of lawyers to recommend. You are subject to the laws of Turkey and the system can be bewildering, so get a good lawyer as soon as possible. And remember, don't do drugs while you are there -- its not worth it.
I was never arrested, but after a serious car accident I did spend several hours at a police station. And I after I lost my US passport, I had some troubel straightening out my visa, leading to a long visit to a different police station, where I was invited to stay until they could work out if I was an illegal immigrant.
