What's the source in the Talmud for the mechitzah? I have yet to run across it.
Also as an aside, I've been to a lot of Synagogues from Talmudic times, and I have yet to find any mechitzah type of division.
Rav Moshe in Igros Moshe 1/1/39 writes that it is based on the Gemorah Sukka 51b Here that a balcony was made in the Beis HaMikdash in order to separate men and women.
I don't have it in front of me, but at the end of "The Silver Era" about Rabbi Eliezer Silver, there is a transcript of how Rabbi Silver proved the halachic need for a Mechitza in court.