How can I become a helicopter pilot?

Would you be willing to change branches? I can only speak for the Army. The Army is at the worst possible moment for trying to bring in new potential aviators. They killed the OH-58D an that left hundreds of qualified aviators out in the cold. They were only able to retrain 1/3 and the rest got kicked directly in the junk. Of the remaining 1/3, they keep getting bumped by senior officers who als have to transition to assume command. The home of Army aviation is Fort Rucker, AL. Go to http://www.army.rucker.mil and look around.

Here's some advice from what I've found out talking to guys who have gone E to O, and those who tried. First off, the most sure way to get a flight school slot is through ROTC, STA-21, or the Naval Academy. These commissioning sources almost exclusively commission unrestricted line officers. Which means the most flight slots go to them. There are slots available for OCS, but you may just as likely end up as a staff officer. If you want to stay in while earning your commission, you can do STA-21 or an enlisted applicant to the Naval Academy. Whatever your course of action, don't let the age cutoff sneak up on you. You must be commissioned by your 28th birthday for a flight school slot. Also, the rate of attrition in flight school varies year to year. They mostly do this in API by raising or lowering the cutoff scores for tests to weed out more or less people depending on the needs of the navy. Best case scenario though, plan on somewhere around 50% of the people starting off flight school with you to not wing. Either due to medical, voluntary drop on request, or slow cutoff scores.

PO2 (Join to see)

I was going to type out a long response to help answer your question as I used to be a Divisional Career Counselor. But ENS Jeremy Medlen gave you the best possible answer for your goals.

The only thing I can add to that is good luck and DO NOT give up on your dream!