This is the question Monica Roberts posed in her column and then to several Trans and bio-ladies that resulted in becoming a 4 part post on her blog. I was honored to be asked for my two cents worth.
The dynamics of female friend relationships are complex anyway. So it's certainly an interesting and worthwhile endeavor to add Transgender women in there. The responses to her questions go a long way in a discussion on understanding and what impedes understanding.
So scroll down to May 2007 Transgriot Column and then check out parts 2-4.
Keep talking ladies.