Sex. vs. Gender - more
In the never-ending (and admittedly futile) battle to get journalists to use the terms sex and gender correctly --and not as synonyms, I offer this "cheat sheet" on Sex vs. Gender from a course on gender and language at Indiana University. (Update December 2011 - thanks to the commenter below who reminded me that the Wayback Machine would probably have a copy, so I have updated the link. In addition, you might find this set of 1993 posts from a women's studies discussion group useful.)
Simply put: Sex is biologically based. Generally just male or female.
Gender: A social construct of what it means to be male or female. So we generally are not looking to determine a crime victim's "gender," as some reporter on TV said the other day. And while a case could be made that it's "gender discrimination" if it's based on a judgment that a person is too feminine or masculine (or not enough) -- generally we're talking about discrimination based on physical attributes. In other words, biologically based, or sex discrimination.