I had a 17 year old girl who I have know for three years come see me after almost a year of not hearing from her and she is 8 months (we think) pregnant and has not seen a dr the entire time she has gotten into meth and is a daily user. She wants me to take full custody of her baby if it survives. I know that the little guy or girl is going to have some major health issues and I am need legal custody so that the mother doesn't take the baby into a bad situation. Where do I start? What do I need to do? TIme is of the essence because we have a month at the most!

I think the best thing is to reach some local lawyer for step by step guidelines, I think this is not a big task as it will be easy for you or anyone. Your thought is correct that you should take the full control legally to save her from any future issues.

If you are in the US, laws vary by state.
The first thing you do is have a DNA test done after the baby is born, so that you can petition Family Court for custody if you are the father. If you are just a concerned friend, you can talk to the hospital social worker when she gives birth. The baby will probably be put in state care immediately. You might be able to be temporary guardian while you work out the child's medical needs and your ability to be a foster parent, or an eventual adopting parent.
You may have 18 years of serious medical and mental problems to deal with.
I wish you could get her to a clinic NOW.

You have two choices, you can foster the child as long as social services agrees or you can adopt the child. In either case, an attempt must be made to locate the child's father to make sure he doesn't object to either.

If she is that far along, then the first thing is to contact social services and let them know you want to foster the child. With a high risk child like this, they may not have a waiting list. Once you get approved as the potential foster, nothing further can be done until the child is born.