There's no post I'm aware of for changing these. I've however seen where people have pulled the keypad and cleaned the contacts and have got them working again.
By the sounds of things as far as your door not staying latched I'd say it's your latch mechanism that appears to be bad.
As far as pulling either of them I couldn't tell you for sure how to pull the door panel in a 04, mine is a 99 and I know it real well but I imagine there's differences. I can tell you that pulling the keypad and door mechanism is kind of a pain.
I'd recommend you purchase a repair manual as these topics are usually covered in them, and for the money they can save you they more than pay for themselves. Another option is the following site that I've heard of others using you can subscribe to for repair information. I haven't used them myself but maybe theres others out here that can tell you more about them.
http://www.alldatadiy.com/