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The problem is that you have two different Publisher articles, and it's not an easy way to do it.
You can still accomplish it by doing this:
1) If you have no module set for the Home page, you can copy the content of one of the articles, and place it in a new custom Block, which you then make visible only to the Anonymous group.
Then you create another Block with the content for Registered users, and make it visible only to the Registered users.
You'll make both Blocks visible only on the "Top Page".
This way the groups will see only what you want them to see on the Home/Main page.
Other option:
2) You can clone Publisher (see the "Clone Module" tab in the Publisher's Admin), to a new module, (you can name it, e.g. "welcome", and create only one article there, the one that you want to use for the Anonymous.
Then you install the "Startup" module mentioned earlier, and set there the new "welcome" module as as starting module for the Anonymous group, and Publisher for Webmasters and Registered Users.
Maybe somebody else will come with a better idea?