How do I tell my friends I have schizophrenia and am going to stay in a psychiatric hospital?

Unashamed. Help educate your friends about mental illness in general and schizophrenia in particular. Hospitalization is a time when your true friends should rally around you. Any friend who would abandon you during a difficult time was not a friend to begin with. Elimination of the stigma of mental illness will happen one relationship at a time. Be strong and unashamed and your good friends will as well.
Consider NAMI. I completely agree with dr. Miller. Right now, you should focus on your health and your recovery, before starting to include your significant others into the process. However, once you are at that stage, you will find that a lot of people struggle with that same question. Nami is an organization that focuses precisely on issues like this one, and they have branches all over the country.
Carefully. Tell only your best friends. Much stigma around "schizophrenia", and there is no need for people to know the details. Simply saying you have a "condition" that you were born with, and that has just begun to express itself, may work. Say it is a neurological condition and that you will be discovering what medication will work best, and thus need to spend a while in the hospital.
Why do you need to? You could say nothing or you could tell them you need extra help at a hospital right now. Sometimes less is more.
Psychiatry Admission. I am not sure that there is one "right" way to handle this. I don't think that you need to feel obligated to share confidential health information. However, your friends can be a valuable support. I would use discretion. Share what you are comfortable with - with whom you are comfortable. Insure that you trust that an individual will maintain your privacy before sharing personal info.
TELL. Tell them you need to get your thoughts and feelings together and youre going to the hospital to pull together and get stable. It takes courage to tell them but if you dont you leave them to worry and not know what to think. Better they should hear from you than make bad guesses. Real friends will remmain friends when youre out.
Depends. If they are truly friends then one would expect them to be supportive during a time of need. Others may need to know little to nothing about your healthcare. What to disclose to whom is an individual decision.
Schizophrenia. Honesty is vital in any friendship, plus they are your support system.
Schizophrenia. In general, I would say that it really no one's business about having schizophrenia. In fact, I suggest to many of my patients, that they say they had to go to the hospital because of problems with headaches, and then just leave it at that. It is very important for you to stay on the medication that is prescribed, so your problems can stay under good control. Good luck.