If you want to know how to help an alcoholic here is what you should do.  Keep in mind that this information I'm giving you has been learned slowly over the years from raw experience....working with struggling alcoholics both on a personal level and also in a professional capacity.  I have many friends who are trying to recover from alcoholism and I also work in a drug and alcohol treatment center, so I have direct experience with this.

First of all, my number one recommendation for anyone trying to help an alcoholic is to first get help themselves.  This might sound a bit strange to you at first because I know your main goal is to see the struggling alcoholic in your life get better.  But quite honestly this is the most important step for you to take at this point, because you have to look out for yourself first and don't allow yourself to fall victim to constant manipulation.  One of the best places to get help is at an Al-Anon meeting.  You can find these by asking around, perhaps call up a local AA club or a treatment center and ask them if they know of any local Al-Anon meetings.  If they do, and you can get to just one, then the people there will be able to fill you in on where all the other Al-Anon meetings are located nearby.

Second of all, I would advice against making ultimatums.  You can set boundaries, and set limits, but if you want to know how to help an alcoholic, then avoid getting into power struggles and setting ultimatums.  This can be a bit of an art form so the people at Al-Anon will be able to help you with this fine balance you are trying to achieve.  Basically, you have to decide what is acceptable behavior to you on the part of the alcoholic in your life, and what is NOT acceptable behavior.  Then, you need to communicate that, simply and plainly to the person.  You also need to outline what your actions will be if they violate your boundaries.  Take the focus off them and put it squarely on yourself if you have to: "This is what I will do if you....."  or "This is how I will respond when you end up in jail again...."  and so on.  Clearly outline what you will and will not do for them in the future.  The main idea to keep in mind here is that you do not want to enable them to continue using.  If they end up in jail then they must suffer the consequences.  If they are hung over and miss work then you should not call in sick for them.

This is not about being spiteful or trying to punish them.  It really is not.  All you are doing is letting them experience their own consequences that they bring on themselves.  There is nothing mean about doing this.  There is nothing spiteful about stepping out of the way and allowing them to fall on their face a few times.  They must reap what they have sown and if you are constantly rescuing them then they will never really learn.

Finally, I would keep in mind that you should never deny an alcoholic of their pain.  If they are actively drinking then their life is fueled by pain, and if you get in the way of that pain then you only prolong their disease and encourage more drinking.  They will never get to that point where they have "had enough" unless they finally experience enough pain in their life.  So learn how to step out of their destructive path and let them experience the pain that they have invited into their life.  It is the only way that they will come to learn the meaning of surrender.  Without this pain, they will continue to keep fighting and struggling to stay drunk.