How can I deal with shyness around women?

I've had this problem since I was a teenager. I was made fun of a lot and my parents sheltered me quite a bit, so talking to women(and speaking up for myself in general, I'm fearful of rejection or conflict), is something I can't do. If a friend of mine introduces me to a girl, I litterally freeze up or just say as little as possible, which has started to draw some ire from my friends, who have all pretty much "mastered" dealing with girls. It's really killing my self-esteem and has started to affect me adversely. I really don't know what to do. I'm a nice guy, but I'm tired of being one, cause I'm starting to see that nice guys do finish last.