np812,
They will take anyone addicted to opiates - it doesn't matter what opiate, as long as it's in your system when you sign up (they test you). Most clinics have a dr, or at least one on call. They usually start you out at around 30 a day until they can adjust your dose to fit with your weight, tolerance, etc. Once you reach a comfortable level you'll go on methadone maintenance until you're psychologically and physically ready to quit, then they will slowly reduce you down. At first you'll have to come in every day, but as you prove trustworthy (no dirty UA's), they'll let you take more and more doses home (up to a months worth). One of the big problems with Methadone, though, is that even after you reduce down, the w/ds can still be very difficult and last a long time.
Good luck