Basically, the easiest way is you have to establish a medical history of chronic pain. Go see a doctor, any doctor, about something that gives you chronic pain. If it's bad enough that it keeps you from sleeping at night, it helps. Let them prescribe you the vicodn or whatever. See if that helps your pain. If it doesn't, go back for another visit with that doctor, and get something else. Now you have established a medical history of chronic pain over probably about a month, ideally.
Now you can go to the pot doctor, at a MAMA clinic,
http://www.mamas.org/Clinics.htm with your ALREADY DIAGNOSED condition (that is a prerequisite) and they will ask you questions, like "Do you think Medical Marijuana will help you with your chronic pain?" or something to that effect, you say yes, they give you paperwork, you send off for your card with some $$ (not sure of amount) and walla, you can smoke, grow, and transport.
Hope this helps!