Just Wondering

I just read this post on Ashley's blog and it reminded me of what I was wondering about yesterday after watching Oprah. In case you didn't watch Oprah yesterday, the episode was about a pregnant "man."

At one point in the show, Oprah mentioned that the "man" and his wife are legally married because s/he had legally become a man. That got me wondering about how one does legally change their sex from female to male. What exactly is the process involved?

Is it just a matter of filling out some paperwork? Or do you have to go before a judge and whip out your new "penis" for inspection? And where is the law that states that a person even can legally change their sex? How did the idea of writing that law even come up?