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There are several ways to do this. Perhaps the easiest is if you want a static center, is to create a custom block using the iframe tag in html to load an outside page. You could then rotate articles, by simply placing a different page in the iframe tag.
Another way is to download on of the modules for this purpose. There are several at:
https://xoops.org/modules/repository/viewcat.php?cid=95 that allow you to rotate articles in a block.