A brief introduction to gender issues, in my understanding.
According to the American Heritage Dictionary:

Sex: (Noun)
1. The property or quality by which organisms are classified as female or male on the basis of their reproductive organs and functions.
2. Either of the two divisions, designated female and male, of this classification.

Gender:

Well, before I start posting the dictionary definition of gender, I'd ask my (limited to nonexistent?) readership to consider what makes up gender. Outside of biology, what makes us men and women? What makes you a man or a woman? The clothes you wear? The way you look? The things you like, your friends, your relationships with other people?

Speaking of, I'd like to recommend an article. Normally I have mixed feeling on the NYT, but I don't totally mind the take this article has on the gender/body bending Thomas Beatie story. There is, of course, a lot left out, but it definitely encourages examining our current standard definitions of gender.