I think that it is more nurture than nature when it comes to attitudes and emotions. I have noticed that I am much more emotional since taking PM, but I don't think my overall brain structure has changed (or that it's even possible at this point.)
We went to the Cleveland Art Museum today, and they had a sound exhibit that was so moving I had tears. This would have never happened pre-PM.
It may be psychosomatic (we want to behave more female, so we do) or it may be that we are less depressed because PM balances something we were lacking. For some the GD goes away (sadly, mine has not yet).
There a few structural differences in the brain... female brains have a thicker corpus collusum which causes better communication between the hemispheres. I doubt PM could change that.
I think it is possible to have a more female brain if the connections were laid down in fetal development. I totally support that there can be men with female brains and females with male brains... I just don't agree that your brain can switch if it wasn't that way already.
Here is a good link to differences:
http://science.howstuffworks.com/life/me...rains1.htm
From a neurology point of view, I think that PM may have an influence on certain neurotransmitters like dopamine and GABA. That's just a theory, though... take it with a grain of salt, please.