I won't be popular for saying this, but women talking trash about other women is the "not so nice" part of our human nature, I am afraid. I am not saying that it's "right", it just *is*.
http://www.oprah.com/tows/pastshows/...20020424.jhtml
They discussed this on Oprah a while ago, and was very interesting. "Odd Girl Out" by Rachel Simmons was the book that addressed this.
Sela Ward even spoke of her experiences:
http://www.oprah.com/tows/pastshows/...020515_b.jhtml