There are several ways. You can use an include bot to do this, that would
probably be the least painful. You can also use Shared Borders, but these
can be problematic and maybe messup the overall look and feel (not to
mention be buggy sometimes). Also you can use DWTs (dynamic web templates)
but these require the most work as it will require you to apply a template
to all your pages and determine which content will go where in the template.
The include bot is probably the least painful as all it entails is for you
to point the include bot to the page that has the content you want to
include in that particular spot. The downside is you must manually insert
the bot onto each page. Unfortunately, there aren't any easier ways to do
this as normally this decision is done in the first design steps before
content is written so you can determine which method you'll need to use to
maintain a consistent look and feel.