You're right. It is a very male dominated field but there is room for talented women in this field as well.
I've been in the financial industry for 8 years and have done quite well - although I left the true "brokerage" side a few years ago to come work for one of those "evil" mutual fund companies

.
My best advice for you is to
be competent and
look competent. A friend of mine who is very competent in her work didn't "look" competent... she's a very pretty girl, at the time was 26, and had long blonde hair and didn't quite look like someone that you'd trust your money to.... she got a new shorter hairstyle, started wearing glasses... new look, new clients, new found respect. It sounds harsh but if you want the part, you've got to play the part.
The male brokers/financial advisors are pretty quick to want to mentor young women that they think have what it takes. Like in many fields, women have to "prove" themselves a little more than men do but it is absolutely possible.
What I've found on the mutual fund side is that there are many more women in Sr. Management roles than what I saw on the brokerage side. The reason I made the switch was to get out of the sales side and move into the support side and an opportunity was waiting for me (due to a little networking on my part).
Good Luck!