I tend to think most homosexuals are born that way. Most not all. The kids I knew that turned out to be gay as adults were pretty gay as kids. At least the men were.
This article and links on the thread explain in detail the causes of homosexuality. And the fact that if a homosexual wants out of the "gay" life, he or she has a good chance of doing so.
http://www.freerepublic.com/focus/f-news/1420619/posts