Everyone has done a good job of explaining the differences but I just wanted to say that most of the first times I went to NA meetings, I went home and got high, sometimes they even made me feel like getting high even more. I realize now though that the problem wasn't with the meetings, it was with my understanding/willingness/denial. I'm just to the point now where that is starting to change and Na meetings are starting to help a lot. It helps when you start to meet other ppl too, and start the program, 12 steps, etc. I have even gone to a couple meetings high/coming down before, but just keep going. I've been going to the odd meeting and considering recovery for months, but now it is finally sinking in and I am getting it.
Some people can get sober with a support group alone, and some people need more. I realized I needed more and I am going to rehab very soon. I'm terrified but I am finally willing to do whatever it takes and I think a lot of the success for a person in rehab, depends on their attitude towards it. If you are willing and want recovery bad enough to give rehab a try, I think you should definitely do it. I am at my wits end with my addiction and I am willing to give anything a try to get better. For me, I realized I need to get away and be in a safe place to deal with all the emotional aftermath of quitting drugs, and get grounded in my recovery. You might need the same thing.