Am I gay for liking pre-op trans-gender women?

If you are attracted to her femininity and consider her to be a woman, then no, you are not gay, whether she's pre-op, post-op or no op. Likewise, if she considers herself a woman and is attracted to you, and you're a man, then she is also straight, even though she was born male. A transgender woman is a woman stuck in a man's body, and a transgender man is a man stuck in a woman's body. So, in other Words, it's a case by case basis.

It matters what gender you identify with and what gender you're attracted to. If the two are the same, then you are homosexual. If the two are different, you are straight. In your case, you are straight.