Kind of makes sense to me Andy, I think its all hormonal and has some to do with DNA. Just like you see these kids with birth defects like 4 arms, or 6 fingers and what not. I bet the same goes for hormones and sex genes getting crossed.
If you are a woman, and somehow your genetics are f-ed up to where your body is pumping out Testosterone and hardly any Estrogen, I can see how you'd feel like a man stuck in a woman's body and vice versa. If that makes sense to what you are wondering.
I don't know how the hell a man could be attracted to another man in the first place, unless the above happens or I guess if you are fed up with the way women act. But women are so f-ing beautiful, I can see how women could be attracted to other women.