...I'm with the "I just am..." crowd on this one.
I'd like to present a meta-viwpoint, if I may. This question comes up a lot in trans circles, but hardly ever amongst the general population. For the 95%+ whose body-gender and mind-gender are well-integrated, it's just not a question. You are what you are, now lets get on to doing other things.
But we transgenders constantly bump up against this dissociation between what our bodies tell society and how 'society' in turn reacts to our bodies, and what we feel internally. Compared to the 95%, I was always asking myself what makes a man a 'man' and a woman a 'woman'. But what blinded me to my own condition was in part that I thought everyone asked these questions of themselves, but (like me,) didn't talk about it much.
Part of my epiphany monologue-to-self went something like this, "You ninny! The answer was there all along! Why didn't you see it until now?!? >whack|whack|whack<"
For my part, my goal is to become the natural me. It's pretty clear that the internal me is a feminine/female/womanly spirit that was strait-jacketed into a 'male' mold and leashed to 'society'-s idea of 'male' behaviour. Am I a woman? (or, the 'woman' that Sheila is asking about?)
No. Yes.
Let me repeat and clarify. My answer to me IS: "No. Yes."
...It's going to be 102 in Sacramento today. I better get my run over and the lawn mowed before I sweat the damn patches right off my derierre...

Karen