Being transgender has nothing to do with sexuality actually, this discussion is actually a bit tangent to the original topic. I mentioned before I'm transgender but I'm a lesbian so I'm attracted to other women, but at birth the doctor assigned me male. Being trans happens when the parts of the brain, which are spread throughout, which determine how we perceive our own gender are so different from what the body turns out as that it creates a dysphoria over the incongruence. These formative periods occur very early in pregnancy, usually within the first to third week. The AMA is actually discussing listing it amongst the other intersex conditions.
Being transgender as an experience is something akin in sensation to being born without a hand but your nervous system contains that hand in its map, so you have the sensation that says, "there's a hand there" or at least "there should be a hand there" but when you look down there's nothing. Except in the case of transgender people this applies to most of our bodies. The problem we deal with most is that instead of the person who doesn't have a hand who receives sympathy and help from society as a whole and the problem is acknowledged, we get told its all in our head, that we're abominations, that we're deceitful, and that we're just really really gay.
That all said, some transgender people, men or women, are straight, attracted to women or men respectively. Others are gay or bisexual or pansexual. The instance of homosexuality in the transgender population is more or less equal to that in the larger population. There is a slightly increased instance of bisexuality but that higher instance is likely due to the "nurture" side of development than anything.
