there are at least two ways to get this result:
1) create a new layout that places this special portlet whereever you want, using the theme's portlet tag
2) add a special layout region to your layout that will host this special portlet. Each page then has to have a window definition for this portlet with the special region name assigned to it. This is how the tabbed navigation is done in the default portal. Take a look.
Note: For the future (2.4) we are thinking about a page inheritence model where such common portlets could be assigned to a page definition that other pages inherit from (so that they inherit the portlet assignments from the parent page)