Natalie,
As you have said that this is a college paper I would like to refer you back to your school. Most schools have an online library for access to scholarly journals. wikipedia and other websites should be avoided as sources to cite because they are not scholarly and as such probably not acceptable to you prof. They are however a great resource for sources if you look at what the wikipedia article or website use as their sources then go look those work up (probably at your school or local library).

As for the big controversy this thread has turned into there are a few things which should be considered. It is right, that in our current time and place a woman wearing pants is not crossdressing. The opposition of acceptability here is not a good one for you paper for many reasons beyond those already stated. But a couple possible lines of thought you can look into are the effects women's movements of the last 50 or so years which have had as one of their main ideals that women can do anything men can - which would include wearing pants. Before the women's liberation movements the enforcement of what types of clothing women wore was as much about women "being in their place" as anything else. It was about what women were supposed to be. Feminism and women's liberation movements have made it, and rightly so, that you can't tell a woman she can't do something on the basis that she is a woman that. The second part you might want to look at is the traditional position of masculine as higher value than feminine in conjunction with western (mostly American) ideals of trying to achieve or succeed. Achievement and success are all about upward mobility therefore, if masculine is above feminine a woman wearing pants is attempting to "improve" while a man wearing a dress is choosing to go downward. This issue can be found in more places than sex/gender such as the fact that a black man trying to pass for white would be more acceptable than a white man trying to pass for black.

Anthropologically speaking, human societies evolved from early beginnings of hunter/gather societies. As such the most valued trait was physical strength as this was the most commonly useful for production and therefore survival. As men are on average stronger than women this "natural inequality" (Rousseau) became associated with men while its opposite, weakness, became associated with women. Hunter/gathers transitioned into farming/herding societies, and then into industrial societies based on physical labour (in some cases where European based societies encountered non-European based hunter/gather societies the farming/herding stage was skipped - i.e.: Coast Salish). In both of these physical strength was again the most useful for production and therefore for survival while the associations of strength with men and weakness with women hadn't changed (men were still on average physically stronger). Homo-sapiens, thus these societies, came into being approximately 200,000 years ago so the trait of strength was the most useful and therefore most valued for a long time. Financial and technological societies, where physical strength is not the most useful quality, are infants in comparison to the length of human existence and as such there is a long history of deeply entrenched values to overcome. In all honestly, the first real wide-spread upheaval of men being more highly valued began only a mere 100 years ago with Vladimir Lenin and Aleksandra Kollontai who argued for, and eventual succeeded in, incorporating women into the industrial workplace on a large scale. However, even within soviet Russia it was considered more socially expectable for a woman to take on a man's role or identity then for a man to take a woman's. There were even cases of women who, known to their superiors, crossdresed and passed to attain high positions in the military or government while men crossdressing was still quite taboo and would have been kept behind closed doors. It is interesting to note, however, that there was no taboo regarding alternative sexualities with the commissar of public affairs, Grigorii Chicherin, one of the most prominent members of Lenin's government being openly gay. (Gender roles and identities in Soviet Russia is a topic I wrote a paper on just last year which I would be willing to share if it will help. It does have some discussion of alternative sexualities and alternative gender identities.)

Anyway, this has been a mouthful but I hope it helps. I know how tough it can be to begin to form your ideas for an academic paper. I am struggling with that for my current work for a theory class I am taking. Sometimes the actual ideas and wording of your topic don't really form until the rest of your paper does.